{
    "29": {
        "question": "What do these two changes have in common?\ncompost rotting\na piece of apple turning brown",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nCompost forms from the remains of plants and animals, such as vegetable scraps and egg shells. Compost rotting is a chemical change. As the compost rots, it breaks down and turns into a different type of matter.\nA piece of apple turning brown is a chemical change. The apple reacts with oxygen in the air and turns into a different type of matter.\nIf you scrape off the brown layer of the apple, the inside is still white. The inside hasn't touched the air. So the chemical change didn't happen to that part of the apple.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "128": {
        "question": "What do these two changes have in common?\nbutter melting on a hot day\nmixing sand and water",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are chemical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nButter melting on a hot day is a change of state. So, it is a physical change. The butter changes from solid to liquid, but it is still made of the same type of matter.\nMixing sand and water is a physical change. Adding water makes the sand wet. But both the sand and water are still made of the same type of matter as before.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nButter melting on a hot day is caused by heating. But mixing sand and water is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "210": {
        "question": "What do these two changes have in common?\ndry ice sublimating and becoming a gas\nburning a marshmallow over a campfire",
        "choices": [
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are chemical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nDry ice is solid carbon dioxide. When dry ice gets warm, it changes state and becomes carbon dioxide gas. This change of state, from solid to gas, is called sublimation.\nDry ice becoming a gas is a physical change. A change of state does not form a different type of matter.\nBurning a marshmallow is a chemical change. The heat from the fire causes the type of matter in the marshmallow to change. The marshmallow becomes black and crispy.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nDry ice sublimating is a physical change. But burning a marshmallow is not.\nBoth are chemical changes.\nBurning a marshmallow is a chemical change. But dry ice sublimating is not.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "214": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a meatball at a temperature of 139°F",
            "a meatball at a temperature of 126°F",
            "a meatball at a temperature of 111°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three meatballs have the same mass but different temperatures. Since the 139°F meatball is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "272": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a cherry pie at a temperature of 100°F",
            "a cherry pie at a temperature of 85°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two cherry pies have the same mass but different temperatures. Since the 100°F pie is hotter than the 85°F pie, it has more thermal energy.",
        "split": "test"
    },
    "363": {
        "question": "Which is bumpier?",
        "choices": [
            "bark",
            "wood ruler"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Bumpy is a property. A bumpy material is covered in lumps and bumps. It is not flat or smooth.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the bark is bumpier. If you could touch this tree bark, it would feel lumpy and bumpy.",
        "split": "test"
    },
    "554": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 200-gram mug of cocoa at a temperature of 155°F",
            "a 200-gram mug of cocoa at a temperature of 115°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two mugs of cocoa have the same mass but different temperatures. Since the 155°F mug of cocoa is hotter than the 115°F mug of cocoa, it has more thermal energy.",
        "split": "test"
    },
    "739": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 7-kilogram block of iron at a temperature of 135°C",
            "a 7-kilogram block of iron at a temperature of 110°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two blocks of iron have the same mass but different temperatures. Since the 135°C block is hotter than the 110°C block, it has more thermal energy.",
        "split": "test"
    },
    "1056": {
        "question": "What do these two changes have in common?\na slice of banana turning brown\nchicken cooking in an oven",
        "choices": [
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA slice of banana turning brown is a chemical change. The part of the banana in contact with the air reacts with oxygen and turns into a different type of matter.\nCooking chicken is a chemical change. The heat causes the matter in the chicken to change. Cooked chicken and raw chicken are different types of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nCooking is caused by heating. But a slice of banana turning brown is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "1286": {
        "question": "What do these two changes have in common?\na piece of pizza rotting in a trashcan\nburning a candle",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA piece of pizza rotting is a chemical change. The matter in the pizza breaks down and slowly turns into a different type of matter.\nBurning a candle is a chemical change. Both the wick and the melted wax burn. They react with oxygen in the air and turn into soot, carbon dioxide, and water.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBurning is caused by heating. But a piece of pizza rotting is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "1531": {
        "question": "Which mug of cider has a lower temperature?",
        "choices": [
            "the mug of cider with less thermal energy",
            "the mug of cider with more thermal energy"
        ],
        "answer": 0,
        "hint": "Two 150-gram mugs of cider are identical except for their thermal energies.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How are temperature and mass related to thermal energy?",
        "lecture": "Matter is made of tiny particles called atoms. Atoms are always moving.\nThe energy of moving atoms is called thermal energy. The total amount of thermal energy in matter depends on three things: the type of matter, the amount of matter, and how fast the atoms are moving.\nTemperature measures how hot or cold matter is. If the atoms in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.\nWhat happens if the amount of matter changes? A 2-kilogram brick at 70°F has twice as much thermal energy as a 1-kilogram brick at 70°F. The two bricks have the same temperature, but the larger brick has twice as many atoms. So, it has twice as much thermal energy.",
        "solution": "The two mugs of cider are made of the same material and have the same mass. So, the mug of cider with less thermal energy has a lower temperature.",
        "split": "test"
    },
    "1621": {
        "question": "What do these two changes have in common?\nbaking cookies\nwater evaporating from a puddle",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking cookies is a chemical change. Cookies are made from cookie dough. Baking turns the cookie dough into cookies. The cookies are a different type of matter than the dough.\nWater evaporating from a puddle is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nWater evaporating is a physical change. But baking cookies is not.\nBoth are chemical changes.\nBaking cookies is a chemical change. But water evaporating from a puddle is not.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "1703": {
        "question": "What do these two changes have in common?\nerosion caused by wind\nice melting in a cup",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nErosion caused by wind is a physical change. The wind carries away tiny pieces of rock. But the pieces of rock do not become a different type of matter.\nIce melting in a cup is a change of state. So, it is a physical change. The solid ice becomes liquid, but it is still made of water.\nThe links between atoms in the water molecules do not change. So, a different type of matter is not formed.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nIce melting is caused by heating. But erosion caused by wind is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "1721": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 120-gram bottle of water at a temperature of 10°C",
            "a 120-gram bottle of water at a temperature of 20°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two bottles of water have the same mass but different temperatures. Since the 10°C bottle of water is colder than the 20°C bottle of water, it has less thermal energy.",
        "split": "test"
    },
    "1784": {
        "question": "What do these two changes have in common?\na piece of pear turning brown\nacid rain weathering a marble statue",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are caused by heating."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA piece of a pear turning brown is a chemical change. The substances in the pear react with oxygen in the air and turn into a different type of matter.\nIf you scrape off the brown part of the pear, the inside will still be white. The inside hasn't touched the air. So the chemical change hasn't happened to that part of the pear.\nAcid rain weathering a marble statue is a chemical change. The acid rain reacts with the outside of the statue and breaks it down into a different type of matter. This new matter is then washed away by the rain. Acid rain is a type of pollution. It forms when smoke from automobiles and factories mixes with water in clouds.\nAcid rain is a type of pollution. It forms when automobiles and factories release smoke containing sulfur or nitrogen. Some of these chemicals react with water in the atmosphere. The reaction forms droplets of water that can fall back to the ground as acid rain.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "1848": {
        "question": "What do these two changes have in common?\nplants making food from sunlight, air, and water\na penny tarnishing",
        "choices": [
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by cooling."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nPlants making food is a chemical change. Plants use energy from sunlight to change air and water into food. The food is sugar. Sugar is a different type of matter than air or water.\nMetal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "2009": {
        "question": "Which object has the least thermal energy?",
        "choices": [
            "a 200-gram cup of black tea at a temperature of 187°F",
            "a 200-gram cup of black tea at a temperature of 154°F",
            "a 200-gram cup of black tea at a temperature of 172°F"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "All three cups of black tea have the same mass but different temperatures. Since the 154°F cup of black tea is the coldest, it has the least thermal energy.",
        "split": "test"
    },
    "2098": {
        "question": "Select the solid.",
        "choices": [
            "air inside a balloon",
            "wet paint",
            "tent"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.\nWhen matter is a gas, it spreads out to fill a space.\nMany gases are invisible. So, you can’t see them. Air is a gas.",
        "solution": "The air inside a balloon is a gas. A gas spreads out to fill a space. The air inside a balloon spreads out to fill all the space in the balloon. If the balloon pops, the air will spread out to fill a much larger space.\nA tent is a solid. You can fold a tent or spread it out. But it will still have a size and shape of its own.\nWet paint is a liquid. A liquid takes the shape of any container it is in. If you pour wet paint out of a can, the paint will change shape. But the wet paint will still take up the same amount of space.",
        "split": "test"
    },
    "2149": {
        "question": "Which would smell more?",
        "choices": [
            "toothpaste",
            "metal car bumper"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Smelly is a property. A smelly material has a strong smell.\nLook at each picture, one at a time. Imagine smelling the material shown in each picture.\nOf the choices, the toothpaste would smell more. Toothpaste has a strong smell.",
        "split": "test"
    },
    "2327": {
        "question": "Which is more flexible?",
        "choices": [
            "diamond",
            "wool sweater"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Flexible is a property. A flexible material can be bent without breaking easily.\nLook at each picture, one at a time. Imagine bending the material shown in each picture.\nOf the choices, the wool sweater is more flexible. If you fold a wool sweater, it will not break.",
        "split": "test"
    },
    "2531": {
        "question": "What do these two changes have in common?\nrust forming on a bike frame\na penny tarnishing",
        "choices": [
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nRust forming on a bike frame is a chemical change. The metal on the bike changes into rust. Metal and rust are different types of matter.\nMetal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "2715": {
        "question": "What do these two changes have in common?\nmaking paper from wood\nroasting a marshmallow over a campfire",
        "choices": [
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMaking paper from wood is a chemical change. Paper is made by mixing tiny pieces of wood with special chemicals. The wood reacts with the chemicals to form pulp. Wood and pulp are different types of matter.\nRoasting a marshmallow is a chemical change. The type of matter on the outside of the marshmallow changes. As a marshmallow is roasted, it turns brown and crispy.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nRoasting is caused by heating. But making paper from wood is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "2731": {
        "question": "Select the mixture.",
        "choices": [
            "beads",
            "oxygen"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Mixtures",
        "skill": "Identify mixtures",
        "lecture": "A pure substance is made of only one type of matter.\nA mixture is made of two or more types of matter mixed together.",
        "solution": "",
        "split": "test"
    },
    "2742": {
        "question": "Which piece of rope has more thermal energy?",
        "choices": [
            "the hotter piece of rope",
            "the colder piece of rope"
        ],
        "answer": 0,
        "hint": "Two 15-gram pieces of rope are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How are temperature and mass related to thermal energy?",
        "lecture": "Matter is made of tiny particles called atoms. Atoms are always moving.\nThe energy of moving atoms is called thermal energy. The total amount of thermal energy in matter depends on three things: the type of matter, the amount of matter, and how fast the atoms are moving.\nTemperature measures how hot or cold matter is. If the atoms in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.\nWhat happens if the amount of matter changes? A 2-kilogram brick at 70°F has twice as much thermal energy as a 1-kilogram brick at 70°F. The two bricks have the same temperature, but the larger brick has twice as many atoms. So, it has twice as much thermal energy.",
        "solution": "The two pieces of rope are made of the same material and have the same mass. So, the hotter piece of rope has more thermal energy.",
        "split": "test"
    },
    "2785": {
        "question": "What do these two changes have in common?\nmilk going sour\nbaking a loaf of bread",
        "choices": [
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMilk going sour is a chemical change. The type of matter in the milk slowly changes. The new matter that is formed gives the milk its sour taste.\nBaking a loaf of bread is a chemical change. Bread is made from dough. Baking turns the dough into bread. The bread is a different type of matter than the dough.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBaking is caused by heating. But milk going sour is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "2900": {
        "question": "What do these two changes have in common?\nice melting in a cup\ndew appearing on grass in the morning",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nIce melting in a cup is a change of state. So, it is a physical change. The solid ice becomes liquid, but it is still made of water.\nThe links between atoms in the water molecules do not change. So, a different type of matter is not formed.\nDew appearing on grass in the morning is a change of state. So, it is a physical change. Water vapor in the air touches the cool grass and becomes liquid.\nThe water vapor changes state to become dew, but it is still made of water. A different type of matter is not formed.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nIce melting is caused by heating. But dew appearing on grass is not.\nBoth are caused by cooling.\nDew appears when water vapor in the air condenses into a liquid on the grass. This is caused by cooling. But ice melting is not.",
        "split": "test"
    },
    "3037": {
        "question": "Which object has the least thermal energy?",
        "choices": [
            "a 250-gram glass of water at a temperature of 29°C",
            "a 250-gram glass of water at a temperature of 14°C",
            "a 250-gram glass of water at a temperature of 16°C"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "All three glasses of water have the same mass but different temperatures. Since the 14°C glass of water is the coldest, it has the least thermal energy.",
        "split": "test"
    },
    "3044": {
        "question": "Select the solid.",
        "choices": [
            "piece of paper",
            "rain",
            "air inside a bubble"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.\nWhen matter is a gas, it spreads out to fill a space.\nMany gases are invisible. So, you can’t see them. Air is a gas.",
        "solution": "Rain is a liquid. A liquid takes the shape of any container it is in. If you put rainwater into a bucket, the rainwater will take the shape of the bucket. But the rainwater will still take up the same amount of space.\nThe air inside a bubble is a gas. A gas spreads out to fill a space. The air inside a bubble fills all the space in the bubble. If the bubble pops, the air will spread out to fill a much larger space.\nA piece of paper is a solid. You can fold a piece of paper. But it will still have a size and shape of its own.",
        "split": "test"
    },
    "3204": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 150-gram glass of apple juice at a temperature of 5°C",
            "a 150-gram glass of apple juice at a temperature of 10°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two glasses of apple juice have the same mass but different temperatures. Since the 5°C glass of apple juice is colder than the 10°C glass of apple juice, it has less thermal energy.",
        "split": "test"
    },
    "3433": {
        "question": "Complete the statement.\nSodium iodide is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 1,
        "hint": "Sodium iodide can be used to help treat certain types of cancer. The chemical formula for sodium iodide is NaI.",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether sodium iodide is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for sodium iodide, NaI, contains two atomic symbols: Na for sodium and I for iodine. So, the formula tells you that sodium iodide is composed of two chemical elements bonded together.\nSince sodium iodide is composed of multiple chemical elements bonded together, sodium iodide is a compound.",
        "split": "test"
    },
    "3472": {
        "question": "Which would smell more?",
        "choices": [
            "metal license plate",
            "gasoline"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Smelly is a property. A smelly material has a strong smell.\nLook at each picture, one at a time. Imagine smelling the material shown in each picture.\nOf the choices, the gasoline would smell more. Gasoline has a strong smell.",
        "split": "test"
    },
    "3498": {
        "question": "Select the mixture.",
        "choices": [
            "caramel corn",
            "silver"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Mixtures",
        "skill": "Identify mixtures",
        "lecture": "A pure substance is made of only one type of matter.\nA mixture is made of two or more types of matter mixed together.",
        "solution": "",
        "split": "test"
    },
    "3504": {
        "question": "What do these two changes have in common?\nwater evaporating from a puddle\ndust settling out of the air",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nWater evaporating from a puddle is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.\nDust settling out of the air is a physical change. As the dust settles, or falls, it might land on furniture or the ground. This separates dust particles from the air, but does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nWater evaporating is caused by heating. But dust settling out of the air is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "3576": {
        "question": "What do these two changes have in common?\nwater evaporating from a lake\nstretching a rubber band",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nWater evaporating from a lake is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.\nStretching a rubber band is a physical change. The rubber band gets longer. But it is still made of the same type of matter as before.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nWater evaporating is caused by heating. But stretching a rubber band is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "3710": {
        "question": "Complete the statement.\nPhosphorus tribromide is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Phosphorus tribromide is used to make certain types of medicine. The chemical formula for phosphorus tribromide is PBr3.",
        "image": null,
        "task": "closed choice",
        "grade": "grade6",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether phosphorus tribromide is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for phosphorus tribromide, PBr3, contains two atomic symbols: P for phosphorus and Br for bromine. So, the formula tells you that phosphorus tribromide is composed of two chemical elements bonded together.\nSince phosphorus tribromide is composed of multiple chemical elements bonded together, phosphorus tribromide is a compound.",
        "split": "test"
    },
    "3973": {
        "question": "Complete the sentence.\nCutting your fingernails is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two ways matter can change.\nIn a chemical change, the type of matter changes.\nBurning a piece of paper is a chemical change. The paper changes into ash and smoke.\nIn a physical change, the type of matter stays the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nIce melting is also a physical change. When ice melts, it changes from a solid to a liquid. But both ice and liquid water are made of the same type of matter: water! This kind of change is called a change of state.",
        "solution": "Cutting your fingernails is a physical change. Your fingernails are shorter after you cut them. But the pieces are still made of the same type of matter as the uncut fingernails.",
        "split": "test"
    },
    "4126": {
        "question": "Which is the hardest?",
        "choices": [
            "rock",
            "clay ball",
            "nylon swim shorts"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Hard is a property. A hard material keeps its shape when you press on it with your finger.\nLook at each picture, one at a time. Imagine pushing on the material shown in each picture.\nOf the choices, the rock is the hardest. If you squeeze a rock, it will not change shape.",
        "split": "test"
    },
    "4145": {
        "question": "Select the mixture.",
        "choices": [
            "salad",
            "sugar"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Mixtures",
        "skill": "Identify mixtures",
        "lecture": "A pure substance is made of only one type of matter.\nA mixture is made of two or more types of matter mixed together.",
        "solution": "",
        "split": "test"
    },
    "4193": {
        "question": "Which is bumpier?",
        "choices": [
            "cardboard",
            "asphalt road"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Bumpy is a property. A bumpy material is covered in lumps and bumps. It is not flat or smooth.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the asphalt road is bumpier. If you touch an asphalt road, it will feel lumpy and bumpy.",
        "split": "test"
    },
    "4210": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 5-kilogram block of iron at a temperature of 75°C",
            "a 5-kilogram block of iron at a temperature of 70°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two blocks of iron have the same mass but different temperatures. Since the 75°C block is hotter than the 70°C block, it has more thermal energy.",
        "split": "test"
    },
    "4282": {
        "question": "What do these two changes have in common?\na penny tarnishing\nan old sandwich rotting in a trashcan",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMetal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.\nA sandwich rotting is a chemical change. The matter in the sandwich breaks down and slowly turns into a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "4285": {
        "question": "Which is softer?",
        "choices": [
            "cotton towel",
            "wood ruler"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Soft is a property. A soft material changes shape when pressed or squeezed.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the cotton towel is softer. If you squeeze cotton fabric, it will change shape.",
        "split": "test"
    },
    "4333": {
        "question": "Select the liquid.",
        "choices": [
            "water from a faucet",
            "stone statue",
            "book",
            "arrowhead"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "An arrowhead is a solid. A solid has a size and shape of its own. An arrowhead is made of rock.\nThe water from a faucet is a liquid. A liquid takes the shape of any container it is in. If you put water from a faucet into a container, the water will take the shape of that container. But the water will still take up the same amount of space.\nA book is a solid. When you read a book, you bend the spine and turn the pages. But the book still has a shape of its own.\nA stone statue is a solid. A solid has a size and shape of its own. Stone statues are made of one or more pieces of rock. Each piece of rock has a size and shape of its own.",
        "split": "test"
    },
    "4502": {
        "question": "Complete the statement.\nHydrogen peroxide is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 1,
        "hint": "Hydrogen peroxide can be used to kill bacteria on medical tools. The chemical formula for hydrogen peroxide is H2O2.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether hydrogen peroxide is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for hydrogen peroxide is H2 O2. This formula contains two symbols: H for hydrogen and O for oxygen. So, the formula tells you that hydrogen peroxide is made of two chemical elements bonded together.\nSubstances made of two or more chemical elements bonded together are compounds. So, hydrogen peroxide is a compound.",
        "split": "test"
    },
    "4603": {
        "question": "What do these two changes have in common?\nmixing chocolate syrup into milk\nstapling an envelope shut",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMixing chocolate syrup into milk is a physical change. The chocolate syrup and milk make a mixture. Making a mixture does not form a different type of matter.\nStapling an envelope shut is a physical change. The envelope and the staple get new shapes. Both are still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "4632": {
        "question": "Complete the sentence.\nIn this chemical reaction, ammonium nitrate is a ().",
        "choices": [
            "reactant",
            "product"
        ],
        "answer": 0,
        "hint": "This passage describes a chemical reaction. Read the passage. Then, follow the instructions below.\nTo help relieve pain during a dental visit, a dentist may give a patient nitrous oxide. Nitrous oxide is made in factories by carefully heating ammonium nitrate. At 170°C, ammonium nitrate breaks down and forms a mixture of nitrous oxide gas and water vapor. After the mixture is collected, the water vapor is separated from the nitrous oxide gas.",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Identify reactants and products",
        "lecture": "A chemical change occurs when new substances are formed from existing substances. This process is called a chemical reaction.\nIn a chemical reaction, one or more substances change into one or more different substances. During the reaction, the atoms of the original substances are rearranged to form other substances.\nThe original substances in a chemical reaction are called reactants. These substances react, or go through a chemical change.\nThe substances that are formed in a chemical reaction are called products. These substances are produced by the chemical reaction.\nSo, in a chemical reaction, reactants go through a chemical change to form products.",
        "solution": "Read the underlined text carefully. Look for information about what happens to ammonium nitrate in this chemical reaction.\nTo help relieve pain during a dental visit, a dentist may give a patient nitrous oxide. Nitrous oxide is made in factories by carefully heating ammonium nitrate. At 170°C, ammonium nitrate breaks down and forms a mixture of nitrous oxide gas and water vapor. After the mixture is collected, the water vapor is separated from the nitrous oxide gas.\nThe underlined text tells you that when ammonium nitrate breaks down, nitrous oxide and water are formed. When ammonium nitrate reacts, or goes through a chemical change, its atoms are rearranged to form nitrous oxide and water. Because ammonium nitrate reacts in this chemical reaction, ammonium nitrate is a reactant.",
        "split": "test"
    },
    "4933": {
        "question": "What do these two changes have in common?\nbaking an apple pie\nplants making food from sunlight, air, and water",
        "choices": [
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking an apple pie is a chemical change. The type of matter in the pie changes. The apples become soft, and the crust turns brown.\nPlants making food is a chemical change. Plants use energy from sunlight to change air and water into food. The food is sugar. Sugar is a different type of matter than air or water.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBaking is caused by heating. But plants making food is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "5032": {
        "question": "Select the liquid.",
        "choices": [
            "chair",
            "baseball",
            "water in a waterfall",
            "air from a hair dryer"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "A baseball is a solid. A solid has a size and shape of its own. If you hit a baseball with a bat, the baseball will still have a size and shape of its own.\nThe air from a hair dryer is a gas. A gas expands to fill a space. A hair dryer uses a fan to blow warm air out. When the air leaves the hair dryer, the air expands to fill a much large space.\nThe water in a waterfall is a liquid. A liquid can change shape. But it still takes up the same amount of space. As water flows down a waterfall, the water changes shape.\nA chair is a solid. A solid has a size and shape of its own. When you sit on a chair, it keeps its shape.",
        "split": "test"
    },
    "5188": {
        "question": "Select the elementary substance.",
        "choices": [
            "pyrite (FeS2)",
            "nickel (Ni)",
            "chloromethane (CH3Cl)"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for pyrite contains two symbols: Fe for iron and S for sulfur. So, pyrite is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, pyrite is a compound, not an elementary substance. The chemical formula for chloromethane contains three symbols: C for carbon, H for hydrogen, and Cl for chlorine. So, chloromethane is made of three chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, chloromethane is a compound, not an elementary substance. The chemical formula for nickel contains one symbol: Ni. So, nickel is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, nickel is an elementary substance.",
        "split": "test"
    },
    "5214": {
        "question": "Which object has the least thermal energy?",
        "choices": [
            "a meatball at a temperature of 51°C",
            "a meatball at a temperature of 44°C",
            "a meatball at a temperature of 53°C"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "All three meatballs have the same mass but different temperatures. Since the 44°C meatball is the coldest, it has the least thermal energy.",
        "split": "test"
    },
    "5418": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 150-gram mug of cider at a temperature of 40°C",
            "a 150-gram mug of cider at a temperature of 30°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two mugs of cider have the same mass but different temperatures. Since the 40°C mug of cider is hotter than the 30°C mug of cider, it has more thermal energy.",
        "split": "test"
    },
    "5475": {
        "question": "What do these two changes have in common?\ntearing a piece of paper\nstapling an envelope shut",
        "choices": [
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are chemical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nTearing a piece of paper is a physical change. The paper tears into pieces. But each piece is still made of paper.\nStapling an envelope shut is a physical change. The envelope and the staple get new shapes. Both are still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "5975": {
        "question": "Which is more flexible?",
        "choices": [
            "tape",
            "plastic ball"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Flexible is a property. A flexible material can be bent without breaking easily.\nLook at each picture, one at a time. Imagine bending the material shown in each picture.\nOf the choices, the tape is more flexible. If you bend a piece of tape, it will not break.",
        "split": "test"
    },
    "5978": {
        "question": "What do these two changes have in common?\nbleaching clothes\na piece of apple turning brown",
        "choices": [
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBleaching clothes is a chemical change. The bleach reacts with dark stains on the clothes. The reaction changes the stains into different types of matter that wash away easily.\nA piece of apple turning brown is a chemical change. The apple reacts with oxygen in the air and turns into a different type of matter.\nIf you scrape off the brown layer of the apple, the inside is still white. The inside hasn't touched the air. So the chemical change didn't happen to that part of the apple.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "6222": {
        "question": "What do these two changes have in common?\na piece of pizza rotting in a trashcan\ncooking an egg",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA piece of pizza rotting is a chemical change. The matter in the pizza breaks down and slowly turns into a different type of matter.\nCooking an egg is a chemical change. The heat causes the matter in the egg to change. Cooked eggs and raw eggs are made of different types of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nCooking is caused by heating. But a piece of pizza rotting is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "6442": {
        "question": "Which is more flexible?",
        "choices": [
            "nylon shorts",
            "ceramic mug"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Flexible is a property. A flexible material can be bent without breaking easily.\nLook at each picture, one at a time. Imagine bending the material shown in each picture.\nOf the choices, the nylon shorts are more flexible. If you fold nylon fabric, it will not break.",
        "split": "test"
    },
    "6470": {
        "question": "Complete the sentence.\nDry ice sublimating and becoming a gas is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade6",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Dry ice is solid carbon dioxide. When dry ice gets warm, it changes state and becomes carbon dioxide gas. This change of state, from solid to gas, is called sublimation.\nDry ice becoming a gas is a physical change. A change of state does not form a different type of matter.",
        "split": "test"
    },
    "6660": {
        "question": "Which brick has more thermal energy?",
        "choices": [
            "the hotter brick",
            "the colder brick"
        ],
        "answer": 0,
        "hint": "Two 2-kilogram bricks are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How are temperature and mass related to thermal energy?",
        "lecture": "Matter is made of tiny particles called atoms. Atoms are always moving.\nThe energy of moving atoms is called thermal energy. The total amount of thermal energy in matter depends on three things: the type of matter, the amount of matter, and how fast the atoms are moving.\nTemperature measures how hot or cold matter is. If the atoms in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.\nWhat happens if the amount of matter changes? A 2-kilogram brick at 70°F has twice as much thermal energy as a 1-kilogram brick at 70°F. The two bricks have the same temperature, but the larger brick has twice as many atoms. So, it has twice as much thermal energy.",
        "solution": "The two bricks are made of the same material and have the same mass. So, the hotter brick has more thermal energy.",
        "split": "test"
    },
    "6763": {
        "question": "Which water balloon has more thermal energy?",
        "choices": [
            "the colder water balloon",
            "the hotter water balloon"
        ],
        "answer": 1,
        "hint": "Two water balloons are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How are temperature and mass related to thermal energy?",
        "lecture": "Matter is made of tiny particles called atoms. Atoms are always moving.\nThe energy of moving atoms is called thermal energy. The total amount of thermal energy in matter depends on three things: the type of matter, the amount of matter, and how fast the atoms are moving.\nTemperature measures how hot or cold matter is. If the atoms in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.\nWhat happens if the amount of matter changes? A 2-kilogram brick at 70°F has twice as much thermal energy as a 1-kilogram brick at 70°F. The two bricks have the same temperature, but the larger brick has twice as many atoms. So, it has twice as much thermal energy.",
        "solution": "The two water balloons are made of the same material and have the same mass. So, the hotter water balloon has more thermal energy.",
        "split": "test"
    },
    "6779": {
        "question": "What do these two changes have in common?\nbaking cookies\na piece of avocado turning brown",
        "choices": [
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are caused by cooling."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking cookies is a chemical change. The type of matter in the cookie dough changes when it is baked. The cookie dough turns into cookies!\nA piece of avocado turning brown is a chemical change. The avocado reacts with oxygen in the air to form a different type of matter.\nIf you scrape off the brown part of the avocado, the inside will still be green. The inside hasn't touched the air. So the chemical change hasn't happened to that part of the avocado.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBaking is caused by heating. But a piece of avocado turning brown is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "7007": {
        "question": "What do these two changes have in common?\nan antacid tablet reacting with water\nburning food on a stove",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nAn antacid tablet reacting with water is a chemical change. When the tablet touches water, the type of matter in the tablet changes and carbon dioxide gas is released. This gas makes the water fizz.\nBurning food on a stove is a chemical change. When the food burns, the type of matter in it changes. The food turns black and gives off smoke.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBurning is caused by heating. But an antacid tablet reacting with water is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "7037": {
        "question": "Complete the sentence.\nRust forming on a bike frame is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two ways matter can change.\nIn a chemical change, the type of matter changes.\nBurning a piece of paper is a chemical change. The paper changes into ash and smoke.\nIn a physical change, the type of matter stays the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nIce melting is also a physical change. When ice melts, it changes from a solid to a liquid. But both ice and liquid water are made of the same type of matter: water! This kind of change is called a change of state.",
        "solution": "Rust forming on a bike frame is a chemical change. The metal on the bike changes into rust. Metal and rust are different types of matter.",
        "split": "test"
    },
    "7085": {
        "question": "What do these two changes have in common?\ncarving a piece of wood\nsewing an apron",
        "choices": [
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nCarving a piece of wood is a physical change. The wood changes shape, but it is still made of the same type of matter.\nSewing an apron is a physical change. The fabric and thread that make up the apron get a new shape, but the type of matter in each of them does not change.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "7092": {
        "question": "Which is the softest?",
        "choices": [
            "plastic bucket",
            "cotton apron",
            "glass flask"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Soft is a property. A soft material changes shape when pressed or squeezed.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the cotton apron is the softest. Cotton fabric changes shape easily when you squeeze it.",
        "split": "test"
    },
    "7150": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 200-gram cup of black tea at a temperature of 105°F",
            "a 200-gram cup of black tea at a temperature of 100°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two cups of black tea have the same mass but different temperatures. Since the 105°F cup of black tea is hotter than the 100°F cup of black tea, it has more thermal energy.",
        "split": "test"
    },
    "7403": {
        "question": "Select the mixture.",
        "choices": [
            "lemonade",
            "silver"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Mixtures",
        "skill": "Identify mixtures",
        "lecture": "A pure substance is made of only one type of matter.\nA mixture is made of two or more types of matter mixed together.",
        "solution": "",
        "split": "test"
    },
    "7415": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a 5-kilogram gold bar at a temperature of 31°F",
            "a 5-kilogram gold bar at a temperature of 17°F",
            "a 5-kilogram gold bar at a temperature of 25°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three gold bars have the same mass but different temperatures. Since the 31°F gold bar is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "7512": {
        "question": "Which is harder?",
        "choices": [
            "rubber balloons",
            "ceramic tea cup"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Hard is a property. A hard material keeps its shape when you press on it with your finger.\nLook at each picture, one at a time. Imagine pushing on the material shown in each picture.\nOf the choices, the ceramic tea cup is harder. If you press on a piece of ceramic, it will not change shape.",
        "split": "test"
    },
    "7533": {
        "question": "Select the mixture.",
        "choices": [
            "oxygen",
            "blocks"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Mixtures",
        "skill": "Identify mixtures",
        "lecture": "A pure substance is made of only one type of matter.\nA mixture is made of two or more types of matter mixed together.",
        "solution": "",
        "split": "test"
    },
    "7625": {
        "question": "Which is stickier?",
        "choices": [
            "paper crane",
            "glue"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Sticky is a property. A sticky material can stick to other things.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the glue is stickier. If you touch wet glue, it will stick to you.",
        "split": "test"
    },
    "7892": {
        "question": "What do these two changes have in common?\nrust forming on a metal gate\nsaliva breaking down a piece of bread",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nRust forming on a metal gate is a chemical change. As the gate rusts, the metal turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.\nSaliva breaking down a piece of bread is a chemical change. Bread is made up mostly of a chemical called starch. Saliva breaks the bonds between atoms in the starch molecules.\nThe atoms then link together to form smaller, simpler molecules of sugar. The sugar is a different type of matter than the starch.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "8022": {
        "question": "What do these two changes have in common?\nburning a candle\ndeep-frying chicken",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBurning a candle is a chemical change. Both the wick and the melted wax burn. They react with oxygen in the air and turn into soot, carbon dioxide, and water.\nDeep-frying chicken is a chemical change. The heat causes the matter in the chicken to change. Cooked chicken and raw chicken are different types of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "8035": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 150-gram glass of orange juice at a temperature of 50°F",
            "a 150-gram glass of orange juice at a temperature of 40°F"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two glasses of orange juice have the same mass but different temperatures. Since the 40°F glass of orange juice is colder than the 50°F glass of orange juice, it has less thermal energy.",
        "split": "test"
    },
    "8100": {
        "question": "What do these two changes have in common?\nbutter melting on a hot day\ncooking an egg",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nButter melting on a hot day is a change of state. So, it is a physical change. The butter changes from solid to liquid, but it is still made of the same type of matter.\nCooking an egg is a chemical change. The heat causes the matter in the egg to change. Cooked egg and raw egg are different types of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nButter melting on a hot day is a physical change. But cooking an egg is not.\nBoth are chemical changes.\nCooking an egg is a chemical change. But butter melting on a hot day is not.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "8321": {
        "question": "What do these two changes have in common?\nbeating an egg\nmixing lettuce and salad dressing",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBeating an egg is a physical change. Beating an egg mixes together the egg white, egg yolk, and some air. But mixing them together does not form a different type of matter.\nMixing lettuce and salad dressing is a physical change. Together, the salad and dressing make a mixture. But making this mixture does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "8515": {
        "question": "What do these two changes have in common?\na copper statue turning green\nfiring a clay pot in a hot kiln",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA copper statue turning green is a chemical change. The copper reacts with oxygen in the air. This reaction forms a different type of matter called copper oxide. The copper oxide is green.\nFiring a clay pot in a hot kiln is a chemical change. High temperatures cause the clay to slowly harden. After several hours in the kiln, the clay will have changed into a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nFiring clay is caused by heating. But a copper statue turning green is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "8749": {
        "question": "What do these two changes have in common?\nsediment settling to the bottom of a muddy puddle\ndry ice sublimating and becoming a gas",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nLoose matter such as sand and dirt is called sediment. Sediment settling to the bottom of a muddy puddle is a physical change.\nThe sediment sinks, and the water above becomes clearer. This separates the water from the sediment. But separating a mixture does not form a different type of matter.\nDry ice is solid carbon dioxide. When dry ice gets warm, it changes state and becomes carbon dioxide gas. This change of state, from solid to gas, is called sublimation.\nDry ice becoming a gas is a physical change. A change of state does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nDry ice sublimating is caused by heating. But sediment settling to the bottom of a muddy puddle is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "8878": {
        "question": "Complete the statement.\nSilicon dioxide is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Silicon dioxide occurs naturally in the mineral quartz, which makes up many of the particles in sand. The chemical formula for silicon dioxide is SiO2.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether silicon dioxide is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for silicon dioxide is SiO2. This formula contains two symbols: Si for silicon and O for oxygen. So, the formula tells you that silicon dioxide is made of two chemical elements bonded together.\nSubstances made of two or more chemical elements bonded together are compounds. So, silicon dioxide is a compound.",
        "split": "test"
    },
    "9005": {
        "question": "Select the elementary substance.",
        "choices": [
            "helium (He)",
            "boron trifluoride (BF3)",
            "fluoromethanol (CH3FO)"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for fluoromethanol contains four symbols: C for carbon, H for hydrogen, F for fluorine, and O for oxygen. So, fluoromethanol is made of four chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, fluoromethanol is a compound, not an elementary substance. The chemical formula for helium contains one symbol: He. So, helium is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, helium is an elementary substance. The chemical formula for boron trifluoride contains two symbols: B for boron and F for fluorine. So, boron trifluoride is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, boron trifluoride is a compound, not an elementary substance.",
        "split": "test"
    },
    "9038": {
        "question": "Which is the most flexible?",
        "choices": [
            "rubber gloves",
            "glass window",
            "rock"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Flexible is a property. A flexible material can be bent without breaking easily.\nLook at each picture, one at a time. Imagine bending the material shown in each picture.\nOf the choices, the rubber gloves are the most flexible. If you gently twist rubber, it will not break.",
        "split": "test"
    },
    "9104": {
        "question": "What do these two changes have in common?\nbaking an apple pie\nusing polish to remove tarnish from a silver spoon",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking an apple pie is a chemical change. The type of matter in the pie changes when it is baked. The crust turns brown, and the apples become soft.\nA tarnished silver spoon is one that has become less shiny over time. Polishing the spoon makes it look shiny again.\nThe polish changes the tarnish into a different type of matter that can be easily wiped away. So, using polish to remove tarnish from silver is a chemical change.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBaking is caused by heating. But polish removing tarnish from a silver spoon is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "9205": {
        "question": "What do these two changes have in common?\nsediment settling to the bottom of a muddy puddle\nan iceberg melting slowly",
        "choices": [
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nLoose matter such as sand and dirt is called sediment. Sediment settling to the bottom of a muddy puddle is a physical change.\nThe sediment sinks, and the water above becomes clearer. This separates the water from the sediment. But separating a mixture does not form a different type of matter.\nAn iceberg melting is a change of state. So, it is a physical change. An iceberg is made of frozen water. As it melts, the water changes from a solid to a liquid. But a different type of matter is not formed.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nAn iceberg melting is caused by heating. But sediment settling to the bottom of a muddy puddle is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "9288": {
        "question": "Which is harder?",
        "choices": [
            "wool scarf",
            "asphalt road"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Hard is a property. A hard material keeps its shape when you press on it with your finger.\nLook at each picture, one at a time. Imagine pushing on the material shown in each picture.\nOf the choices, the asphalt road is harder. If you step on asphalt, it will not change shape.",
        "split": "test"
    },
    "9295": {
        "question": "Complete the sentence.\nIn this chemical reaction, water is a ().",
        "choices": [
            "reactant",
            "product"
        ],
        "answer": 1,
        "hint": "This passage describes a chemical reaction. Read the passage. Then, follow the instructions below.\nHydrogen peroxide, a household disinfectant, breaks down into water and oxygen gas over time. Light speeds up this process, so hydrogen peroxide is typically stored in a dark-colored bottle. The bottle's dark coloring blocks light and makes the hydrogen peroxide last longer.",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Identify reactants and products",
        "lecture": "A chemical change occurs when new substances are formed from existing substances. This process is called a chemical reaction.\nIn a chemical reaction, one or more substances change into one or more different substances. During the reaction, the atoms of the original substances are rearranged to form other substances.\nThe original substances in a chemical reaction are called reactants. These substances react, or go through a chemical change.\nThe substances that are formed in a chemical reaction are called products. These substances are produced by the chemical reaction.\nSo, in a chemical reaction, reactants go through a chemical change to form products.",
        "solution": "Read the underlined text carefully. Look for information about what happens to water in this chemical reaction.\nHydrogen peroxide, a household disinfectant, breaks down into water and oxygen gas over time. Light speeds up this process, so hydrogen peroxide is typically stored in a dark-colored bottle. The bottle's dark coloring blocks light and makes the hydrogen peroxide last longer.\nThe underlined text tells you that hydrogen forms when hydrogen peroxide breaks down. Because water is produced by this chemical reaction, water is a product.",
        "split": "test"
    },
    "9352": {
        "question": "Complete the statement.\nCyclooctasulfur is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 1,
        "hint": "Cyclooctasulfur is used in the production of rubber bands and automobile tires. The chemical formula for cyclooctasulfur is S8.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether cyclooctasulfur is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for cyclooctasulfur, S8, contains one atomic symbol: S for sulfur. So, the formula tells you that cyclooctasulfur is composed of only one chemical element.\nSince cyclooctasulfur is composed of only one chemical element, cyclooctasulfur is an elementary substance.",
        "split": "test"
    },
    "9394": {
        "question": "What do these two changes have in common?\na puddle freezing into ice on a cold night\nmixing sand and water",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA puddle freezing into ice on a cold night is a change of state. So, it is a physical change. Liquid water freezes and becomes solid, but it is still made of water. A different type of matter is not formed.\nMixing sand and water is a physical change. Adding water makes the sand wet. But both the sand and water are still made of the same type of matter as before.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nA puddle freezing is caused by cooling. But mixing sand and water is not.",
        "split": "test"
    },
    "9475": {
        "question": "Complete the statement.\nPotassium hydroxide is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Potassium hydroxide is used to make liquid soap. The chemical formula for potassium hydroxide is KOH.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether potassium hydroxide is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for potassium hydroxide, KOH, contains three atomic symbols: K for potassium, O for oxygen, and H for hydrogen. So, the formula tells you that potassium hydroxide is composed of three chemical elements bonded together.\nSince potassium hydroxide is composed of multiple chemical elements bonded together, potassium hydroxide is a compound.",
        "split": "test"
    },
    "9509": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 240-gram bottle of water at a temperature of 25°C",
            "a 240-gram bottle of water at a temperature of 10°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two bottles of water have the same mass but different temperatures. Since the 25°C bottle of water is hotter than the 10°C bottle of water, it has more thermal energy.",
        "split": "test"
    },
    "9548": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 250-gram baked potato at a temperature of 60°C",
            "a 250-gram baked potato at a temperature of 40°C"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two baked potatoes have the same mass but different temperatures. Since the 40°C potato is colder than the 60°C potato, it has less thermal energy.",
        "split": "test"
    },
    "9620": {
        "question": "What do these two changes have in common?\nmixing sand and water\ncarving a piece of wood",
        "choices": [
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by cooling."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMixing sand and water is a physical change. Adding water makes the sand wet. But both the sand and water are still made of the same type of matter as before.\nCarving a piece of wood is a physical change. The wood changes shape, but it is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "9650": {
        "question": "Complete the statement.\nHydrogen is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 1,
        "hint": "Hydrogen gas was once used to make large airships, such as blimps, float. It is no longer used in airships because it catches fire easily. The chemical formula for hydrogen is H2.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether hydrogen is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for hydrogen, H2, contains one atomic symbol: H. So, the formula tells you that hydrogen is composed of only one chemical element.\nSince hydrogen is composed of only one chemical element, hydrogen is an elementary substance.",
        "split": "test"
    },
    "9712": {
        "question": "Which baked potato has a lower temperature?",
        "choices": [
            "the baked potato with more thermal energy",
            "the baked potato with less thermal energy"
        ],
        "answer": 1,
        "hint": "Two 200-gram baked potatoes are identical except for their thermal energies.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How are temperature and mass related to thermal energy?",
        "lecture": "Matter is made of tiny particles called atoms. Atoms are always moving.\nThe energy of moving atoms is called thermal energy. The total amount of thermal energy in matter depends on three things: the type of matter, the amount of matter, and how fast the atoms are moving.\nTemperature measures how hot or cold matter is. If the atoms in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.\nWhat happens if the amount of matter changes? A 2-kilogram brick at 70°F has twice as much thermal energy as a 1-kilogram brick at 70°F. The two bricks have the same temperature, but the larger brick has twice as many atoms. So, it has twice as much thermal energy.",
        "solution": "The two baked potatoes are made of the same material and have the same mass. So, the baked potato with less thermal energy has a lower temperature.",
        "split": "test"
    },
    "9744": {
        "question": "Select the solid.",
        "choices": [
            "grape juice",
            "water from a faucet",
            "air from a hair dryer",
            "screwdriver"
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "The air from a hair dryer is a gas. A gas expands to fill a space. A hair dryer uses a fan to blow warm air out. When the air leaves the hair dryer, the air expands to fill a much large space.\nThe water from a faucet is a liquid. A liquid takes the shape of any container it is in. If you put water from a faucet into a container, the water will take the shape of that container. But the water will still take up the same amount of space.\nA screwdriver is a solid. A solid has a size and shape of its own. This screwdriver has a metal blade and a plastic handle. Both metal and plastic are solids.\nGrape juice is a liquid. A liquid takes the shape of any container it is in. If you pour grape juice into a different container, the grape juice will take the shape of that container. But the grape juice will still take up the same amount of space.",
        "split": "test"
    },
    "9915": {
        "question": "Select the mixture.",
        "choices": [
            "cereal",
            "carbon"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Mixtures",
        "skill": "Identify mixtures",
        "lecture": "A pure substance is made of only one type of matter.\nA mixture is made of two or more types of matter mixed together.",
        "solution": "",
        "split": "test"
    },
    "9993": {
        "question": "Which is more flexible?",
        "choices": [
            "rock wall",
            "clay ball"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Flexible is a property. A flexible material can be bent without breaking easily.\nLook at each picture, one at a time. Imagine bending the material shown in each picture.\nOf the choices, the clay ball is more flexible. If you squeeze a ball of wet clay, it will not break easily.",
        "split": "test"
    },
    "10103": {
        "question": "What do these two changes have in common?\nbaking a loaf of bread\nmelting glass",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking a loaf of bread is a chemical change. The type of matter in the dough changes when it is baked. The dough turns into bread!\nMelting glass is a change of state. So, it is a physical change. The glass changes from solid to liquid. But a different type of matter is not formed.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nMelting glass is a physical change. But baking bread is not.\nBoth are chemical changes.\nBaking bread is a chemical change. But melting glass is not.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "10155": {
        "question": "Select the elementary substance.",
        "choices": [
            "methane (CH4)",
            "water (H2O)",
            "zinc (Zn)"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for water contains two symbols: H for hydrogen and O for oxygen. So, water is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, water is a compound, not an elementary substance. The chemical formula for zinc contains one symbol: Zn. So, zinc is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, zinc is an elementary substance. The chemical formula for methane contains two symbols: C for carbon and H for hydrogen. So, methane is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, methane is a compound, not an elementary substance.",
        "split": "test"
    },
    "10352": {
        "question": "What do these two changes have in common?\nsnails growing shells\nphotosynthesis",
        "choices": [
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by cooling."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nSnails growing shells is a chemical change. A snail's body uses calcium from its food to make a new molecule called calcium carbonate. This calcium carbonate is used to grow the shell.\nPhotosynthesis is a chemical change. Plants make sugar using carbon dioxide, water, and energy from sunlight.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "10476": {
        "question": "What do these two changes have in common?\nmixing sand and gravel\ncrushing a mineral into powder",
        "choices": [
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMixing sand and gravel is a physical change. Together, the sand and gravel make a mixture. But making this mixture does not form a different type of matter.\nCrushing a mineral into powder is a physical change. The mineral breaks into tiny pieces. But it is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "10565": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 200-gram glass of grape juice at a temperature of 15°C",
            "a 200-gram glass of grape juice at a temperature of 5°C"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two glasses of grape juice have the same mass but different temperatures. Since the 5°C glass of grape juice is colder than the 15°C glass of grape juice, it has less thermal energy.",
        "split": "test"
    },
    "10623": {
        "question": "What do these two changes have in common?\na puddle freezing into ice on a cold night\nbeating an egg",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA puddle freezing into ice on a cold night is a change of state. So, it is a physical change. Liquid water freezes and becomes solid, but it is still made of water. A different type of matter is not formed.\nBeating an egg is a physical change. Beating an egg mixes together the egg white, egg yolk, and some air. But mixing them together does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nA puddle freezing is caused by cooling. But beating an egg is not.",
        "split": "test"
    },
    "10894": {
        "question": "Which is smoother?",
        "choices": [
            "burlap sack",
            "cardboard"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Smooth is a property. A smooth material is not rough or bumpy.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the cardboard is smoother. If you touch a cardboard box like this one, it will not feel rough or bumpy.",
        "split": "test"
    },
    "11006": {
        "question": "What do these two changes have in common?\nusing polish to remove tarnish from a silver spoon\na piece of avocado turning brown",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA tarnished silver spoon is one that has become less shiny over time. Polishing the spoon makes it look shiny again.\nThe polish changes the tarnish into a different type of matter that can be easily wiped away. So, using polish to remove tarnish from silver is a chemical change.\nA piece of avocado turning brown is a chemical change. The avocado reacts with oxygen in the air to form a different type of matter.\nIf you scrape off the brown part of the avocado, the inside will still be green. The inside hasn't touched the air. So the chemical change hasn't happened to that part of the avocado.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "11206": {
        "question": "Complete the statement.\nPotassium chloride is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Potassium chloride can be added to food as a substitute for table salt. The chemical formula for potassium chloride is KCl.",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether potassium chloride is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for potassium chloride, KCl, contains two atomic symbols: K for potassium and Cl for chlorine. So, the formula tells you that potassium chloride is composed of two chemical elements bonded together.\nSince potassium chloride is composed of multiple chemical elements bonded together, potassium chloride is a compound.",
        "split": "test"
    },
    "11218": {
        "question": "Complete the sentence.\nChicken cooking in an oven is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Cooking chicken is a chemical change. The heat causes the matter in the chicken to change. Cooked chicken and raw chicken are different types of matter.",
        "split": "test"
    },
    "11480": {
        "question": "What do these two changes have in common?\nsewing an apron\nmixing lettuce and salad dressing",
        "choices": [
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by cooling."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nSewing an apron is a physical change. The fabric and thread that make up the apron get a new shape, but the type of matter in each of them does not change.\nMixing lettuce and salad dressing is a physical change. Together, the salad and dressing make a mixture. But making this mixture does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "11901": {
        "question": "Select the liquid.",
        "choices": [
            "umbrella",
            "rain",
            "plate",
            "helium"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "Rain is a liquid. A liquid takes the shape of any container it is in. If you put rainwater into a bucket, the rainwater will take the shape of the bucket. But the rainwater will still take up the same amount of space.\nA plate is a solid. If someone drops a plate, it may break into pieces. But each piece will still have a size and shape of its own.\nAn umbrella is a solid. A solid has a size and shape of its own. When you open an umbrella, it still has a size and shape of its own.\nHelium is a gas. A gas expands to fill a space. Helium is lighter than air. So, if you fill a balloon with helium, the balloon will rise. If helium leaks out of the balloon, the helium will expand into the space around the balloon.",
        "split": "test"
    },
    "11925": {
        "question": "Complete the sentence.\nBreaking a plate is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two ways matter can change.\nIn a chemical change, the type of matter changes.\nBurning a piece of paper is a chemical change. The paper changes into ash and smoke.\nIn a physical change, the type of matter stays the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nIce melting is also a physical change. When ice melts, it changes from a solid to a liquid. But both ice and liquid water are made of the same type of matter: water! This kind of change is called a change of state.",
        "solution": "Breaking a plate is a physical change. The plate gets broken into pieces. But each piece is still made of the same type of matter.",
        "split": "test"
    },
    "11943": {
        "question": "Select the liquid.",
        "choices": [
            "rag doll",
            "eraser",
            "arrowhead",
            "vinegar"
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "An arrowhead is a solid. A solid has a size and shape of its own. An arrowhead is made of rock.\nAn eraser is a solid. You can bend an eraser. But it will still have a size and shape of its own.\nVinegar is a liquid. A liquid takes the shape of any container it is in. If you pour vinegar into a different container, the vinegar will take the shape of that container. But the vinegar will still take up the same amount of space.\nA rag doll is a solid. A solid has a size and shape of its own. When you hold a rag doll in your hands, the rag doll still has a size and shape of its own.",
        "split": "test"
    },
    "12064": {
        "question": "Complete the sentence.\nLeaves changing color in the fall is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Leaves changing color is a chemical change. Leaves contain a chemical called chlorophyll that makes them green. In the fall, the chlorophyll in the leaves changes into a different type of matter.",
        "split": "test"
    },
    "12123": {
        "question": "What do these two changes have in common?\nwater evaporating from a puddle\nrain forming in a cloud",
        "choices": [
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nWater evaporating from a puddle is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.\nRain forming in a cloud is a change of state. So, it is a physical change. Water vapor in the air condenses into tiny droplets of liquid water. These droplets make up a cloud. When there is enough water in the air, the droplets will fall as rain.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nWater evaporating is caused by heating. But rain forming in a cloud is not.\nBoth are caused by cooling.\nRain begins to form when water vapor in the air becomes liquid water. This is caused by cooling. But water evaporating from a puddle is not.",
        "split": "test"
    },
    "12321": {
        "question": "What do these two changes have in common?\ncutting a piece of rope\npeeling a banana",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nCutting a piece of rope is a physical change. The rope is shorter after you cut it. But it is still made of the same type of matter as the uncut rope.\nPeeling a banana is a physical change. The peel is not covering the rest of the fruit anymore. But both the peel and the banana are still made of the same type of matter as before.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "12399": {
        "question": "What do these two changes have in common?\ncooking an egg\na penny tarnishing",
        "choices": [
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nCooking an egg is a chemical change. The heat causes the matter in the egg to change. Cooked egg and raw egg are different types of matter.\nMetal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nCooking is caused by heating. But a penny tarnishing is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "12468": {
        "question": "Select the solid.",
        "choices": [
            "water in a sink",
            "grape juice",
            "baseball bat"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids and liquids",
        "lecture": "Solid and liquid are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.",
        "solution": "",
        "split": "test"
    },
    "12549": {
        "question": "Complete the statement.\nNitrogen is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 1,
        "hint": "Nitrogen gas makes up nearly 80% of the air you breathe. The chemical formula for nitrogen is N2.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether nitrogen is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for nitrogen, N2, contains one atomic symbol: N. So, the formula tells you that nitrogen is composed of only one chemical element.\nSince nitrogen is composed of only one chemical element, nitrogen is an elementary substance.",
        "split": "test"
    },
    "12554": {
        "question": "What do these two changes have in common?\nerosion caused by wind\nbeating an egg",
        "choices": [
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nErosion caused by wind is a physical change. The wind carries away tiny pieces of rock. But the pieces of rock do not become a different type of matter.\nBeating an egg is a physical change. Beating an egg mixes together the egg white, egg yolk, and some air. But mixing them together does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "12606": {
        "question": "Complete the sentence.\nWater evaporating from a puddle is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nA change of state is a type of physical change. For example, ice melting is a physical change. Ice and liquid water are made of the same type of matter: water.",
        "solution": "Water evaporating from a puddle is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.",
        "split": "test"
    },
    "12677": {
        "question": "What do these two changes have in common?\ndry ice sublimating and becoming a gas\nwater freezing into ice",
        "choices": [
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by cooling."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nDry ice is solid carbon dioxide. When dry ice gets warm, it changes state and becomes carbon dioxide gas. This change of state, from solid to gas, is called sublimation.\nDry ice becoming a gas is a physical change. A change of state does not form a different type of matter.\nWater freezing into ice is a change of state. So, it is a physical change. The water changes from solid to liquid. But the ice is still made of the same type of matter as the liquid water.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nDry ice sublimating is caused by heating. But water freezing into ice is not.\nBoth are caused by cooling.\nWater freezing is caused by cooling. But dry ice sublimating is not.",
        "split": "test"
    },
    "12722": {
        "question": "Complete the sentence.\nBees making honey from nectar is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Bees making honey from nectar is a chemical change. The bees use nectar to make honey, which contains new molecules that are easier to store. Honey and nectar are different types of matter.",
        "split": "test"
    },
    "12824": {
        "question": "What do these two changes have in common?\nbreaking a ceramic plate\nknitting yarn into a scarf",
        "choices": [
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBreaking a ceramic plate is a physical change. The plate gets broken into pieces. But each piece is still made of the same type of matter.\nKnitting yarn into a scarf is a physical change. The yarn gets a different shape, but it is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "12869": {
        "question": "What do these two changes have in common?\nwater evaporating from a puddle\nmelting glass",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nWater evaporating from a puddle is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.\nMelting glass is a change of state. So, it is a physical change. The glass changes from solid to liquid. But a different type of matter is not formed.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "12875": {
        "question": "Select the elementary substance.",
        "choices": [
            "hydrogen sulfide (H2S)",
            "cyclopropane (C3H6)",
            "silver (Ag)"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for cyclopropane contains two symbols: C for carbon and H for hydrogen. So, cyclopropane is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, cyclopropane is a compound, not an elementary substance. The chemical formula for silver contains one symbol: Ag. So, silver is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, silver is an elementary substance. The chemical formula for hydrogen sulfide contains two symbols: H for hydrogen and S for sulfur. So, hydrogen sulfide is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, hydrogen sulfide is a compound, not an elementary substance.",
        "split": "test"
    },
    "12878": {
        "question": "Complete the statement.\nArgon is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 0,
        "hint": "Argon is a gas used to protect important documents, including the United States Constitution, from decay. The chemical formula for argon is Ar.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether argon is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for argon is Ar. This formula contains one symbol: Ar. So, the formula tells you that argon is made of one chemical element.\nSubstances made of only one chemical element are elementary substances. So, argon is an elementary substance.",
        "split": "test"
    },
    "12894": {
        "question": "Complete the statement.\nGallium arsenide is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Gallium arsenide is found in the solar cells that power the robotic vehicles used by scientists to explore Mars. The chemical formula for gallium arsenide is GaAs.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether gallium arsenide is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for gallium arsenide, GaAs, contains two atomic symbols: Ga for gallium and As for arsenic. So, the formula tells you that gallium arsenide is composed of two chemical elements bonded together.\nSince gallium arsenide is composed of multiple chemical elements bonded together, gallium arsenide is a compound.",
        "split": "test"
    },
    "13007": {
        "question": "What do these two changes have in common?\na banana getting ripe on the counter\nsaliva breaking down a piece of bread",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA banana getting ripe on the counter is a chemical change. As a banana ripens, the type of matter in it changes. The peel changes color and the inside becomes softer and sweeter.\nSaliva breaking down a piece of bread is a chemical change. Bread is made up mostly of a chemical called starch. Saliva breaks the bonds between atoms in the starch molecules.\nThe atoms then link together to form smaller, simpler molecules of sugar. The sugar is a different type of matter than the starch.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "13210": {
        "question": "What do these two changes have in common?\ngetting a haircut\nsawing a log in half",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nGetting a haircut is a physical change. Your hair is shorter after a haircut. But it is still made of the same type of matter.\nSawing a log in half is a physical change. The log splits into two pieces. But the pieces are still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "13420": {
        "question": "Complete the statement.\nLithium bromide is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Lithium bromide is used to absorb moisture from the air. The chemical formula for lithium bromide is LiBr.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether lithium bromide is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for lithium bromide, LiBr, contains two atomic symbols: Li for lithium and Br for bromine. So, the formula tells you that lithium bromide is composed of two chemical elements bonded together.\nSince lithium bromide is composed of multiple chemical elements bonded together, lithium bromide is a compound.",
        "split": "test"
    },
    "13424": {
        "question": "Select the solid.",
        "choices": [
            "coffee",
            "eraser",
            "air inside a tire",
            "air inside a bubble"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "Coffee is a liquid. A liquid takes the shape of any container it is in. If you pour coffee into a different container, the coffee will take the shape of that container. But the coffee will still take up the same amount of space.\nThe air inside a tire is a gas. A gas expands to fill a space. The air in a tire expands to fill all the space inside the tire. If air leaks out, it will expand into the space around the tire.\nThe air inside a bubble is a gas. A gas expands to fill a space. The air inside a bubble fills all the space in the bubble. If the bubble pops, the air will expand to fill a much larger space.\nAn eraser is a solid. You can bend an eraser. But it will still have a size and shape of its own.",
        "split": "test"
    },
    "13525": {
        "question": "Complete the sentence.\nWater freezing into ice is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two ways matter can change.\nIn a chemical change, the type of matter changes.\nBurning a piece of paper is a chemical change. The paper changes into ash and smoke.\nIn a physical change, the type of matter stays the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nIce melting is also a physical change. When ice melts, it changes from a solid to a liquid. But both ice and liquid water are made of the same type of matter: water! This kind of change is called a change of state.",
        "solution": "Water freezing into ice is a change of state. So, it is a physical change. The water changes from solid to liquid. But the ice is still made of the same type of matter as the liquid water.",
        "split": "test"
    },
    "13696": {
        "question": "Which is harder?",
        "choices": [
            "glass bottle",
            "wool scarf"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Hard is a property. A hard material keeps its shape when you press on it with your finger.\nLook at each picture, one at a time. Imagine pushing on the material shown in each picture.\nOf the choices, the glass bottle is harder. If you squeeze a glass bottle, it will not change shape.",
        "split": "test"
    },
    "13856": {
        "question": "Which object has the least thermal energy?",
        "choices": [
            "a marble at a temperature of 60°F",
            "a marble at a temperature of 32°F",
            "a marble at a temperature of 14°F"
        ],
        "answer": 2,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "All three marbles have the same mass but different temperatures. Since the 14°F marble is the coldest, it has the least thermal energy.",
        "split": "test"
    },
    "13872": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 5-kilogram brick at a temperature of 260°F",
            "a 5-kilogram brick at a temperature of 235°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two bricks have the same mass but different temperatures. Since the 260°F brick is hotter than the 235°F brick, it has more thermal energy.",
        "split": "test"
    },
    "13932": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 250-gram cup of black tea at a temperature of 120°F",
            "a 250-gram cup of black tea at a temperature of 115°F"
        ],
        "answer": 1,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two cups of black tea have the same mass but different temperatures. Since the 115°F cup of black tea is colder than the 120°F cup of black tea, it has less thermal energy.",
        "split": "test"
    },
    "13985": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 350-gram mug of cocoa at a temperature of 30°C",
            "a 350-gram mug of cocoa at a temperature of 65°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two mugs of cocoa have the same mass but different temperatures. Since the 30°C mug of cocoa is colder than the 65°C mug of cocoa, it has less thermal energy.",
        "split": "test"
    },
    "14324": {
        "question": "What do these two changes have in common?\nbreaking a ceramic plate\nmixing chocolate syrup into milk",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBreaking a ceramic plate is a physical change. The plate gets broken into pieces. But each piece is still made of the same type of matter.\nMixing chocolate syrup into milk is a physical change. The chocolate syrup and milk make a mixture. Making a mixture does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "14355": {
        "question": "Complete the statement.\nPlatinum is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 0,
        "hint": "Platinum is a precious metal used to make jewelry. The chemical formula for platinum is Pt.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether platinum is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for platinum is Pt. This formula contains one symbol: Pt. So, the formula tells you that platinum is made of one chemical element.\nSubstances made of only one chemical element are elementary substances. So, platinum is an elementary substance.",
        "split": "test"
    },
    "14456": {
        "question": "Select the elementary substance.",
        "choices": [
            "bromomethane (CH3Br)",
            "hydrogen peroxide (H2O2)",
            "rhenium (Re)"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for bromomethane contains three symbols: C for carbon, H for hydrogen, and Br for bromine. So, bromomethane is made of three chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, bromomethane is a compound, not an elementary substance. The chemical formula for rhenium contains one symbol: Re. So, rhenium is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, rhenium is an elementary substance. The chemical formula for hydrogen peroxide contains two symbols: H for hydrogen and O for oxygen. So, hydrogen peroxide is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, hydrogen peroxide is a compound, not an elementary substance.",
        "split": "test"
    },
    "14607": {
        "question": "Complete the statement.\nSodium bromide is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Sodium bromide can be used to kill bacteria in swimming pools. The chemical formula for sodium bromide is NaBr.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether sodium bromide is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for sodium bromide, NaBr, contains two atomic symbols: Na for sodium and Br for bromine. So, the formula tells you that sodium bromide is composed of two chemical elements bonded together.\nSince sodium bromide is composed of multiple chemical elements bonded together, sodium bromide is a compound.",
        "split": "test"
    },
    "14919": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a 175-gram glass of apple juice at a temperature of 65°F",
            "a 175-gram glass of apple juice at a temperature of 40°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two glasses of apple juice have the same mass but different temperatures. Since the 65°F glass of apple juice is hotter than the 40°F glass of apple juice, it has more thermal energy.",
        "split": "test"
    },
    "14941": {
        "question": "What do these two changes have in common?\nsediment settling to the bottom of a muddy puddle\nshaking up salad dressing",
        "choices": [
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by cooling."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nLoose matter such as sand and dirt is called sediment. Sediment settling to the bottom of a muddy puddle is a physical change.\nThe sediment sinks, and the water above becomes clearer. This separates the water from the sediment. But separating a mixture does not form a different type of matter.\nShaking up salad dressing is a physical change. The different parts mix together, but they are still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "14957": {
        "question": "Which would stretch more?",
        "choices": [
            "rubber band",
            "ceramic flower pot"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Stretchy is a property. A stretchy material gets longer when you pull on it.\nLook at each picture, one at a time. Imagine pulling on the material shown in each picture.\nOf the choices, the rubber band would stretch more. If you pull on a rubber band, it will get longer.",
        "split": "test"
    },
    "15105": {
        "question": "Select the liquid.",
        "choices": [
            "water in a fishbowl",
            "chalk",
            "gold bracelet"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids and liquids",
        "lecture": "Solid and liquid are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.",
        "solution": "",
        "split": "test"
    },
    "15253": {
        "question": "Select the elementary substance.",
        "choices": [
            "chloromethane (CH3Cl)",
            "calcium (Ca)",
            "phosphine (PH3)"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for chloromethane contains three symbols: C for carbon, H for hydrogen, and Cl for chlorine. So, chloromethane is made of three chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, chloromethane is a compound, not an elementary substance. The chemical formula for calcium contains one symbol: Ca. So, calcium is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, calcium is an elementary substance. The chemical formula for phosphine contains two symbols: P for phosphorus and H for hydrogen. So, phosphine is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, phosphine is a compound, not an elementary substance.",
        "split": "test"
    },
    "15282": {
        "question": "Which object has more thermal energy?",
        "choices": [
            "a cherry pie at a temperature of 110°F",
            "a cherry pie at a temperature of 80°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "The two cherry pies have the same mass but different temperatures. Since the 110°F pie is hotter than the 80°F pie, it has more thermal energy.",
        "split": "test"
    },
    "15327": {
        "question": "Complete the sentence.\nCellular respiration is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade6",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Cellular respiration is a chemical change. Cells use oxygen to break down sugar. Breaking the chemical bonds in sugar molecules releases energy that a cell can use.\nThe atoms from the broken molecules then combine to form different molecules such as carbon dioxide and water. These molecules are different types of matter than sugar and oxygen.",
        "split": "test"
    },
    "15382": {
        "question": "What do these two changes have in common?\nwater boiling on a stove\nice melting in a glass",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nWater boiling on the stove is a change of state. So, it is a physical change. The liquid changes into a gas, but a different type of matter is not formed.\nIce melting in a glass is a change of state. So, it is a physical change. The solid ice becomes liquid, but it is still made of water. A different type of matter is not made.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "15487": {
        "question": "Select the solid.",
        "choices": [
            "coffee",
            "wet paint",
            "chalk"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.\nWhen matter is a gas, it spreads out to fill a space.\nMany gases are invisible. So, you can’t see them. Air is a gas.",
        "solution": "Wet paint is a liquid. A liquid takes the shape of any container it is in. If you pour wet paint out of a can, the paint will change shape. But the wet paint will still take up the same amount of space.\nChalk is a solid. You can easily break chalk into pieces. But each piece will still have a size and shape of its own.\nCoffee is a liquid. A liquid takes the shape of any container it is in. If you pour coffee into a different container, the coffee will take the shape of that container. But the coffee will still take up the same amount of space.",
        "split": "test"
    },
    "15552": {
        "question": "Complete the sentence.\nIn this chemical reaction, nitrous oxide is a ().",
        "choices": [
            "reactant",
            "product"
        ],
        "answer": 1,
        "hint": "This passage describes a chemical reaction. Read the passage. Then, follow the instructions below.\nTo help relieve pain during a dental visit, a dentist may give a patient nitrous oxide. Nitrous oxide is made in factories by carefully heating ammonium nitrate. At 170°C, ammonium nitrate breaks down and forms a mixture of nitrous oxide gas and water vapor. After the mixture is collected, the water vapor is separated from the nitrous oxide gas.",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Identify reactants and products",
        "lecture": "A chemical change occurs when new substances are formed from existing substances. This process is called a chemical reaction.\nIn a chemical reaction, one or more substances change into one or more different substances. During the reaction, the atoms of the original substances are rearranged to form other substances.\nThe original substances in a chemical reaction are called reactants. These substances react, or go through a chemical change.\nThe substances that are formed in a chemical reaction are called products. These substances are produced by the chemical reaction.\nSo, in a chemical reaction, reactants go through a chemical change to form products.",
        "solution": "Read the underlined text carefully. Look for information about what happens to nitrous oxide in this chemical reaction.\nTo help relieve pain during a dental visit, a dentist may give a patient nitrous oxide. Nitrous oxide is made in factories by carefully heating ammonium nitrate. At 170°C, ammonium nitrate breaks down and forms a mixture of nitrous oxide gas and water vapor. After the mixture is collected, the water vapor is separated from the nitrous oxide gas.\nThe underlined text tells you that nitrous oxide forms when ammonium nitrate breaks down. Because nitrous oxide is produced by this chemical reaction, nitrous oxide is a product.",
        "split": "test"
    },
    "15556": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a crayon at a temperature of 91°F",
            "a crayon at a temperature of 53°F",
            "a crayon at a temperature of 41°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three crayons have the same mass but different temperatures. Since the 91°F crayon is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "15794": {
        "question": "What do these two changes have in common?\nrust forming on a metal gate\nburning food on a stove",
        "choices": [
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nRust forming on a metal gate is a chemical change. As the gate rusts, the metal turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.\nBurning food on a stove is a chemical change. When the food burns, the type of matter in it changes. The food turns black and gives off smoke.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBurning is caused by heating. But rust forming on a metal gate is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "15807": {
        "question": "What do these two changes have in common?\nmixing sand and water\nsediment settling to the bottom of a muddy puddle",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMixing sand and water is a physical change. Adding water makes the sand wet. But both the sand and water are still made of the same type of matter as before.\nLoose matter such as sand and dirt is called sediment. Sediment settling to the bottom of a muddy puddle is a physical change.\nThe sediment sinks, and the water above becomes clearer. This separates the water from the sediment. But separating a mixture does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "15874": {
        "question": "What do these two changes have in common?\nmelting wax\nknitting yarn into a scarf",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are caused by cooling."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMelting wax is a change of state. So, it is a physical change. The wax changes from solid to liquid. But it is still made of the same type of matter.\nKnitting yarn into a scarf is a physical change. The yarn gets a different shape, but it is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nWax melting is caused by heating. But knitting yarn is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "15900": {
        "question": "What do these two changes have in common?\nbreaking a ceramic plate\nwater vapor condensing on a bathroom mirror",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBreaking a ceramic plate is a physical change. The plate gets broken into pieces. But each piece is still made of the same type of matter.\nWater vapor condensing on a bathroom mirror is a change of state. So, it is a physical change. The water changes state from gas in the air to liquid water on the mirror. But the water vapor and the liquid water are both made of water.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nWater vapor condensing is caused by cooling. But breaking a ceramic plate is not.",
        "split": "test"
    },
    "15978": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 5-kilogram brick at a temperature of 385°F",
            "a 5-kilogram brick at a temperature of 390°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two bricks have the same mass but different temperatures. Since the 385°F brick is colder than the 390°F brick, it has less thermal energy.",
        "split": "test"
    },
    "15984": {
        "question": "Which is smoother?",
        "choices": [
            "plastic bucket",
            "burlap sack"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Smooth is a property. A smooth material is not rough or bumpy.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the plastic bucket is smoother. If you touch a plastic bucket like this one, it will not feel rough.",
        "split": "test"
    },
    "16186": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "an orange at a temperature of 64°F",
            "an orange at a temperature of 57°F",
            "an orange at a temperature of 68°F"
        ],
        "answer": 2,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three oranges have the same mass but different temperatures. Since the 68°F orange is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "16338": {
        "question": "Which would stretch the most?",
        "choices": [
            "glass bottle",
            "rubber balloons",
            "diamond"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Stretchy is a property. A stretchy material gets longer when you pull on it.\nLook at each picture, one at a time. Imagine pulling on the material shown in each picture.\nOf the choices, the rubber balloons would stretch the most. If you pull on a rubber balloon, it will get longer.",
        "split": "test"
    },
    "16660": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a 150-gram glass of orange juice at a temperature of 26°C",
            "a 150-gram glass of orange juice at a temperature of 7°C",
            "a 150-gram glass of orange juice at a temperature of 6°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three glasses of orange juice have the same mass but different temperatures. Since the 26°C glass of orange juice is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "16678": {
        "question": "What do these two changes have in common?\na penny tarnishing\na dinosaur bone turning into rock over millions of years",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMetal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.\nA dinosaur bone turning into rock is a chemical change. The matter that made up the bone when it was alive begins to break down. Over a long time, a different type of matter starts forming inside small gaps in the bone. The matter is made of minerals from the earth.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "16754": {
        "question": "Which object has the least thermal energy?",
        "choices": [
            "a meatball at a temperature of 22°C",
            "a meatball at a temperature of 27°C",
            "a meatball at a temperature of 20°C"
        ],
        "answer": 2,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "All three meatballs have the same mass but different temperatures. Since the 20°C meatball is the coldest, it has the least thermal energy.",
        "split": "test"
    },
    "16788": {
        "question": "Which would stretch the most?",
        "choices": [
            "gold crown",
            "plastic water pitcher",
            "cotton head band"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Stretchy is a property. A stretchy material gets longer when you pull on it.\nLook at each picture, one at a time. Imagine pulling on the material shown in each picture.\nOf the choices, the cotton head band would stretch the most. If you pull the ends of a cotton headband, it will get longer.",
        "split": "test"
    },
    "16837": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a crayon at a temperature of 15°C",
            "a crayon at a temperature of 11°C",
            "a crayon at a temperature of 8°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three crayons have the same mass but different temperatures. Since the 15°C crayon is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "16855": {
        "question": "Complete the statement.\nSilver is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 0,
        "hint": "Silver is a precious metal that is used to make many items, such as jewelry and coins. The chemical formula for silver is Ag.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether silver is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for silver is Ag. This formula contains one symbol: Ag. So, the formula tells you that silver is made of one chemical element.\nSubstances made of only one chemical element are elementary substances. So, silver is an elementary substance.",
        "split": "test"
    },
    "16903": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a bowl of oatmeal at a temperature of 35°C",
            "a bowl of oatmeal at a temperature of 40°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two bowls of oatmeal have the same mass but different temperatures. Since the 35°C bowl of oatmeal is colder than the 40°C bowl of oatmeal, it has less thermal energy.",
        "split": "test"
    },
    "17135": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a 2-kilogram brick at a temperature of 458°F",
            "a 2-kilogram brick at a temperature of 430°F",
            "a 2-kilogram brick at a temperature of 453°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three bricks have the same mass but different temperatures. Since the 458°F brick is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "17204": {
        "question": "Select the solid.",
        "choices": [
            "grape juice",
            "spoon",
            "rain"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids and liquids",
        "lecture": "Solid and liquid are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.",
        "solution": "",
        "split": "test"
    },
    "17209": {
        "question": "What do these two changes have in common?\ndeep-frying chicken\nburning a marshmallow over a campfire",
        "choices": [
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nDeep-frying chicken is a chemical change. The heat causes the matter in the chicken to change. Cooked chicken and raw chicken are different types of matter.\nBurning a marshmallow is a chemical change. The heat from the fire causes the type of matter in the marshmallow to change. The marshmallow becomes black and crispy.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "17215": {
        "question": "Complete the sentence.\nBaking cookies is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two ways matter can change.\nIn a chemical change, the type of matter changes.\nBurning a piece of paper is a chemical change. The paper changes into ash and smoke.\nIn a physical change, the type of matter stays the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nIce melting is also a physical change. When ice melts, it changes from a solid to a liquid. But both ice and liquid water are made of the same type of matter: water! This kind of change is called a change of state.",
        "solution": "Baking cookies is a chemical change. Cookies are made from cookie dough. Baking turns the cookie dough into cookies. The cookies are a different type of matter than the dough.",
        "split": "test"
    },
    "17219": {
        "question": "What do these two changes have in common?\na piece of apple turning brown\ncompost rotting",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA piece of apple turning brown is a chemical change. The apple reacts with oxygen in the air and turns into a different type of matter.\nIf you scrape off the brown layer of the apple, the inside is still white. The inside hasn't touched the air. So the chemical change didn't happen to that part of the apple.\nCompost forms from the remains of plants and animals, such as vegetable scraps and egg shells. Compost rotting is a chemical change. As the compost rots, it breaks down and turns into a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "17304": {
        "question": "Complete the sentence.\nRust forming on a bicycle frame is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Rust forming on a bicycle frame is a chemical change. Oxygen in the air reacts with iron in the bicycle frame. The outside of the frame turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.",
        "split": "test"
    },
    "17391": {
        "question": "Complete the sentence.\nA can of soda fizzing over is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "A can of soda fizzing over is a physical change. The soda fizzes because the gas trapped inside of it comes out very quickly. But the types of matter the soda and gas are made of do not change.",
        "split": "test"
    },
    "17435": {
        "question": "What do these two changes have in common?\nusing polish to remove tarnish from a silver spoon\na dinosaur bone turning into rock over millions of years",
        "choices": [
            "Both are chemical changes.",
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA tarnished silver spoon is one that has become less shiny over time. Polishing the spoon makes it look shiny again.\nThe polish changes the tarnish into a different type of matter that can be easily wiped away. So, using polish to remove tarnish from silver is a chemical change.\nA dinosaur bone turning into rock is a chemical change. The matter that made up the bone when it was alive begins to break down. Over a long time, a different type of matter starts forming inside small gaps in the bone. The matter is made of minerals from the earth.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "17441": {
        "question": "Which drop of dish soap has less thermal energy?",
        "choices": [
            "the colder drop of dish soap",
            "the hotter drop of dish soap"
        ],
        "answer": 0,
        "hint": "Two drops of dish soap are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How are temperature and mass related to thermal energy?",
        "lecture": "Matter is made of tiny particles called atoms. Atoms are always moving.\nThe energy of moving atoms is called thermal energy. The total amount of thermal energy in matter depends on three things: the type of matter, the amount of matter, and how fast the atoms are moving.\nTemperature measures how hot or cold matter is. If the atoms in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.\nWhat happens if the amount of matter changes? A 2-kilogram brick at 70°F has twice as much thermal energy as a 1-kilogram brick at 70°F. The two bricks have the same temperature, but the larger brick has twice as many atoms. So, it has twice as much thermal energy.",
        "solution": "The two drops of dish soap are made of the same material and have the same mass. So, the colder drop of dish soap has less thermal energy.",
        "split": "test"
    },
    "17600": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a cherry pie at a temperature of 41°C",
            "a cherry pie at a temperature of 34°C",
            "a cherry pie at a temperature of 48°C"
        ],
        "answer": 2,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three cherry pies have the same mass but different temperatures. Since the 48°C pie is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "17611": {
        "question": "What do these two changes have in common?\nmelting wax\nrain forming in a cloud",
        "choices": [
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nMelting wax is a change of state. So, it is a physical change. The wax changes from solid to liquid. But it is still made of the same type of matter.\nRain forming in a cloud is a change of state. So, it is a physical change. Water vapor in the air condenses into tiny droplets of liquid water. These droplets make up a cloud. When there is enough water in the air, the droplets will fall as rain.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nWax melting is caused by heating. But rain forming in a cloud is not.\nBoth are caused by cooling.\nRain begins to form when water vapor in the air becomes liquid water. This is caused by cooling. But melting wax is not.",
        "split": "test"
    },
    "17688": {
        "question": "Complete the sentence.\nSnowflakes forming in a cloud is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Snowflakes forming in a cloud is a change of state. So, it is a physical change. Liquid water freezes and becomes solid, but it is still made of water. A different type of matter is not formed.",
        "split": "test"
    },
    "17753": {
        "question": "Complete the sentence.\nA dinosaur bone turning into rock over millions of years is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "A dinosaur bone turning into rock is a chemical change. The matter that made up the bone when it was alive begins to break down. Over a long time, a different type of matter starts forming inside small gaps in the bone. The matter is made of minerals from the earth.",
        "split": "test"
    },
    "17797": {
        "question": "Complete the statement.\nSodium chloride is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 1,
        "hint": "Sodium chloride, commonly known as table salt, is used to prevent roads from getting icy. The chemical formula for sodium chloride is NaCl.",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.\nA substance may be composed of one chemical element or multiple chemical elements. Substances that are composed of only one chemical element are elementary substances. Substances that are composed of multiple chemical elements bonded together are compounds.\nEvery chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.\nThe atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one atomic symbol.\nThe atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.\nFor example, the chemical formula for the elementary substance oxygen, O2, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O2 and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple atomic symbols.\nThe chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF2. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.",
        "solution": "You can tell whether sodium chloride is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for sodium chloride, NaCl, contains two atomic symbols: Na for sodium and Cl for chlorine. So, the formula tells you that sodium chloride is composed of two chemical elements bonded together.\nSince sodium chloride is composed of multiple chemical elements bonded together, sodium chloride is a compound.",
        "split": "test"
    },
    "17901": {
        "question": "What do these two changes have in common?\nbending a paper clip\ncutting your fingernails",
        "choices": [
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are chemical changes.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBending a paper clip is a physical change. After you bend it, the paper clip has a different shape. But it is still made of the same type of matter.\nCutting your fingernails is a physical change. Your fingernails are shorter after you cut them. But the pieces are still made of the same type of matter as the uncut fingernails.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "17952": {
        "question": "Select the elementary substance.",
        "choices": [
            "krypton (Kr)",
            "potassium nitrate (KNO3)",
            "sulfur dioxide (SO2)"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Identify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for sulfur dioxide contains two symbols: S for sulfur and O for oxygen. So, sulfur dioxide is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, sulfur dioxide is a compound, not an elementary substance. The chemical formula for krypton contains one symbol: Kr. So, krypton is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, krypton is an elementary substance. The chemical formula for potassium nitrate contains three symbols: K for potassium, N for nitrogen, and O for oxygen. So, potassium nitrate is made of three chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, potassium nitrate is a compound, not an elementary substance.",
        "split": "test"
    },
    "18036": {
        "question": "What do these two changes have in common?\ncrushing a mineral into powder\ndry ice sublimating and becoming a gas",
        "choices": [
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are caused by cooling."
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nCrushing a mineral into powder is a physical change. The mineral breaks into tiny pieces. But it is still made of the same type of matter.\nDry ice is solid carbon dioxide. When dry ice gets warm, it changes state and becomes carbon dioxide gas. This change of state, from solid to gas, is called sublimation.\nDry ice becoming a gas is a physical change. A change of state does not form a different type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nDry ice sublimating is caused by heating. But crushing a mineral is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "18072": {
        "question": "Complete the sentence.\nBeating an egg is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Beating an egg is a physical change. Beating an egg mixes together the egg white, egg yolk, and some air. But mixing them together does not form a different type of matter.",
        "split": "test"
    },
    "18124": {
        "question": "Select the gas.",
        "choices": [
            "air from a hair dryer",
            "tortoise shell",
            "caramel sauce",
            "pair of dice"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "The air from a hair dryer is a gas. A gas expands to fill a space. A hair dryer uses a fan to blow warm air out. When the air leaves the hair dryer, the air expands to fill a much large space.\nA tortoise shell is a solid. A solid has a size and shape of its own. A tortoise shell is made of a solid called keratin, just like your fingernails!\nA pair of dice is a solid. A solid has a size and shape of its own. When you roll a pair of dice, the dice have a shape of their own. They are still cubes when they stop rolling.\nCaramel sauce is a liquid. A liquid takes the shape of any container it is in. If you pour caramel sauce into a container, the caramel sauce will take the shape of that container. But the caramel sauce will still take up the same amount of space.",
        "split": "test"
    },
    "18257": {
        "question": "Which object has the least thermal energy?",
        "choices": [
            "a cherry pie at a temperature of 77°F",
            "a cherry pie at a temperature of 106°F",
            "a cherry pie at a temperature of 113°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "All three cherry pies have the same mass but different temperatures. Since the 77°F pie is the coldest, it has the least thermal energy.",
        "split": "test"
    },
    "18303": {
        "question": "Complete the sentence.\nIn this chemical reaction, zinc oxide is a ().",
        "choices": [
            "product",
            "reactant"
        ],
        "answer": 0,
        "hint": "This passage describes a chemical reaction. Read the passage. Then, follow the instructions below.\nMany watches are powered by small, flat batteries called button cells. One common type of button cell contains the metal zinc. When zinc in the battery combines with oxygen in the air, zinc oxide forms. This process generates the electricity that powers the watch.",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Identify reactants and products",
        "lecture": "A chemical change occurs when new substances are formed from existing substances. This process is called a chemical reaction.\nIn a chemical reaction, one or more substances change into one or more different substances. During the reaction, the atoms of the original substances are rearranged to form other substances.\nThe original substances in a chemical reaction are called reactants. These substances react, or go through a chemical change.\nThe substances that are formed in a chemical reaction are called products. These substances are produced by the chemical reaction.\nSo, in a chemical reaction, reactants go through a chemical change to form products.",
        "solution": "Read the underlined text carefully. Look for information about what happens to zinc oxide in this chemical reaction.\nMany watches are powered by small, flat batteries called button cells. One common type of button cell contains the metal zinc. When zinc in the battery combines with oxygen in the air, zinc oxide forms. This process generates the electricity that powers the watch.\nThe underlined text tells you that zinc oxide forms when zinc combines with oxygen. Because zinc oxide is produced by this chemical reaction, zinc oxide is a product.",
        "split": "test"
    },
    "18328": {
        "question": "Select the solid.",
        "choices": [
            "clothespin",
            "wet paint",
            "grape juice"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids and liquids",
        "lecture": "Solid and liquid are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a shape of its own.\nSome solids can be bent or broken easily. Others are hard to bend or break.\nA glass cup is a solid. A sock is also a solid.\nWhen matter is a liquid, it takes the shape of its container.\nThink about pouring a liquid from a cup into a bottle. The shape of the liquid is different in the cup than in the bottle. But the liquid still takes up the same amount of space.\nJuice is a liquid. Honey is also a liquid.",
        "solution": "",
        "split": "test"
    },
    "18412": {
        "question": "Select the liquid.",
        "choices": [
            "plate",
            "gold bracelet",
            "apple juice",
            "tortoise shell"
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "A tortoise shell is a solid. A solid has a size and shape of its own. A tortoise shell is made of a solid called keratin, just like your fingernails!\nApple juice is a liquid. A liquid takes the shape of any container it is in. If you pour apple juice into a different container, the apple juice will take the shape of that container. But the apple juice will still take up the same amount of space.\nA plate is a solid. If someone drops a plate, it may break into pieces. But each piece will still have a size and shape of its own.\nA gold bracelet is a solid. You can wrap a gold bracelet around your wrist. But the bracelet will still have a size and shape of its own.",
        "split": "test"
    },
    "18892": {
        "question": "What do these two changes have in common?\ncutting an apple\na sidewalk heating up in the sun",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nCutting an apple is a physical change. The apple gets a different shape. But it is still made of the same type of matter as the uncut apple.\nA sidewalk heating up in the sun is a physical change. The temperature of the sidewalk goes up, but the sidewalk is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nA sidewalk getting warm in the sun is caused by heating. But cutting an apple is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "19034": {
        "question": "Which is scratchier?",
        "choices": [
            "bark",
            "rubber ball"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Scratchy is a property. A scratchy material is rough and itchy against your skin.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the bark is scratchier. If you could touch this tree bark, it would feel rough and itchy.",
        "split": "test"
    },
    "19143": {
        "question": "What do these two changes have in common?\na piece of avocado turning brown\nboiling sugar to make caramel",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nA piece of avocado turning brown is a chemical change. The avocado reacts with oxygen in the air to form a different type of matter.\nIf you scrape off the brown part of the avocado, the inside will still be green. The inside hasn't touched the air. So the chemical change hasn't happened to that part of the avocado.\nBoiling sugar to make caramel is a chemical change. The heat causes the sugar to change into a different type of matter. Unlike sugar, the new matter is brown and sticky.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBoiling sugar is caused by heating. But a piece of avocado turning brown is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "19550": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a 150-gram baked potato at a temperature of 43°C",
            "a 150-gram baked potato at a temperature of 40°C",
            "a 150-gram baked potato at a temperature of 26°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three baked potatoes have the same mass but different temperatures. Since the 43°C potato is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "19618": {
        "question": "What do these two changes have in common?\nshaking up salad dressing\nbreaking a piece of glass",
        "choices": [
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nShaking up salad dressing is a physical change. The different parts mix together, but they are still made of the same type of matter.\nBreaking a piece of glass is a physical change. The glass gets broken into pieces. But each piece is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "19678": {
        "question": "Which is smoother?",
        "choices": [
            "rock wall",
            "glass marbles"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade2",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells.",
        "solution": "Smooth is a property. A smooth material is not rough or bumpy.\nLook at each picture, one at a time. Imagine touching the material shown in each picture.\nOf the choices, the glass marbles are smoother. Glass marbles do not feel rough or bumpy when you touch them.",
        "split": "test"
    },
    "19725": {
        "question": "Complete the statement.\nPropane is ().",
        "choices": [
            "an elementary substance",
            "a compound"
        ],
        "answer": 1,
        "hint": "Propane is used as fuel for heaters, engines, and outdoor grills. The chemical formula for propane is C3H8.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether propane is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for propane is C3 H8. This formula contains two symbols: C for carbon and H for hydrogen. So, the formula tells you that propane is made of two chemical elements bonded together.\nSubstances made of two or more chemical elements bonded together are compounds. So, propane is a compound.",
        "split": "test"
    },
    "19778": {
        "question": "Select the solid.",
        "choices": [
            "hair clip",
            "water in a fishbowl",
            "air inside a raft",
            "helium"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "The water in a fishbowl is a liquid. A liquid takes the shape of any container it is in. If you pour water from a fishbowl into a different container, the water will take the shape of that container. But the water will still take up the same amount of space.\nA hair clip is a solid. A solid has a size and shape of its own. You can use a hair clip to keep your hair out of your face because the hair clip keeps its shape.\nThe air inside a raft is a gas. A gas expands to fill a space. The air in a raft expands to fill all the space inside the raft. If air leaks out, it will expand into the space around the raft.\nHelium is a gas. A gas expands to fill a space. Helium is lighter than air. So, if you fill a balloon with helium, the balloon will rise. If helium leaks out of the balloon, the helium will expand into the space around the balloon.",
        "split": "test"
    },
    "19798": {
        "question": "Select the liquid.",
        "choices": [
            "chocolate syrup",
            "ballet shoes",
            "tortoise shell",
            "hair clip"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "A hair clip is a solid. A solid has a size and shape of its own. You can use a hair clip to keep your hair out of your face because the hair clip keeps its shape.\nA ballet shoe is a solid. A solid has a size and shape of its own. When a dancer wears a ballet shoe, it may bend a little. But the ballet shoe still has a size and shape of its own.\nChocolate syrup is a liquid. A liquid takes the shape of any container it is in. If you pour chocolate syrup into a container, the chocolate syrup will take the shape of that container. But the chocolate syrup will still take up the same amount of space.\nA tortoise shell is a solid. A solid has a size and shape of its own. A tortoise shell is made of a solid called keratin, just like your fingernails!",
        "split": "test"
    },
    "19818": {
        "question": "What do these two changes have in common?\nbaking an apple pie\nmaking jam",
        "choices": [
            "Both are only physical changes.",
            "Both are caused by cooling.",
            "Both are caused by heating."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade7",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking an apple pie is a chemical change. The type of matter in the pie changes when it is baked. The crust turns brown, and the apples become soft.\nMaking jam is a chemical change. It involves mixing fruit, sugar, and a substance called pectin.\nWhen these ingredients are mixed and cooked, the chemical bonds in their molecules are broken. The atoms then link together to form different molecules that make up the jam.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBoth changes are caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "19905": {
        "question": "Complete the statement.\nPotassium nitrate is ().",
        "choices": [
            "a compound",
            "an elementary substance"
        ],
        "answer": 0,
        "hint": "Potassium nitrate can be combined with fuels to make powerful explosions. So, it is often used in gunpowder and fireworks. The chemical formula for potassium nitrate is KNO3.",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Atoms and molecules",
        "skill": "Classify elementary substances and compounds using chemical formulas",
        "lecture": "Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.\nEvery chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.\nThe symbol for each element in a substance is shown in the substance's chemical formula.\nAn elementary substance is represented by a chemical formula that contains only one symbol.\nThe symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.\nFor example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.\nThe chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.\nA compound is represented by a chemical formula that contains multiple symbols.\nFor example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.",
        "solution": "You can tell whether potassium nitrate is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.\nThe chemical formula for potassium nitrate is KNO3. This formula contains three symbols: K for potassium, N for nitrogen, and O for oxygen. So, the formula tells you that potassium nitrate is made of three chemical elements bonded together.\nSubstances made of two or more chemical elements bonded together are compounds. So, potassium nitrate is a compound.",
        "split": "test"
    },
    "19990": {
        "question": "Select the solid.",
        "choices": [
            "slide",
            "air inside a bubble",
            "air inside a soccer ball",
            "rain"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "Rain is a liquid. A liquid takes the shape of any container it is in. If you put rainwater into a bucket, the rainwater will take the shape of the bucket. But the rainwater will still take up the same amount of space.\nThe air inside a soccer ball is a gas. A gas expands to fill a space. The air fills all the space inside the soccer ball. If air leaks out, it will expand into the space around the ball.\nThe air inside a bubble is a gas. A gas expands to fill a space. The air inside a bubble fills all the space in the bubble. If the bubble pops, the air will expand to fill a much larger space.\nA slide is a solid. A solid has a size and shape of its own. A slide has a size and shape of its own, even when you sit on it.",
        "split": "test"
    },
    "20134": {
        "question": "What do these two changes have in common?\nwater freezing into ice\nbending a paper clip",
        "choices": [
            "Both are caused by heating.",
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nWater freezing into ice is a change of state. So, it is a physical change. The water changes from solid to liquid. But the ice is still made of the same type of matter as the liquid water.\nBending a paper clip is a physical change. After you bend it, the paper clip has a different shape. But it is still made of the same type of matter.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nWater freezing is caused by cooling. But bending a paper clip is not.",
        "split": "test"
    },
    "20161": {
        "question": "Select the liquid.",
        "choices": [
            "screwdriver",
            "air inside a balloon",
            "hammer",
            "grape juice"
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "States of matter",
        "skill": "Identify solids, liquids, and gases",
        "lecture": "Solid, liquid, and gas are states of matter. Matter is anything that takes up space. Matter can come in different states, or forms.\nWhen matter is a solid, it has a definite volume and a definite shape. So, a solid has a size and shape of its own.\nSome solids can be easily folded, bent, or broken. A piece of paper is a solid. Also, some solids are very small. A grain of sand is a solid.\nWhen matter is a liquid, it has a definite volume but not a definite shape. So, a liquid has a size of its own, but it does not have a shape of its own. Think about pouring juice from a bottle into a cup. The juice still takes up the same amount of space, but it takes the shape of the bottle.\nSome liquids do not pour as easily as others. Honey and milk are both liquids. But pouring honey takes more time than pouring milk.\nWhen matter is a gas, it does not have a definite volume or a definite shape. A gas expands, or gets bigger, until it completely fills a space. A gas can also get smaller if it is squeezed into a smaller space.\nMany gases are invisible. Air is a gas.",
        "solution": "The air inside a balloon is a gas. A gas expands to fill a space. The air inside a balloon expands to fill all the space in the balloon. If the balloon pops, the air will expand to fill a much larger space.\nGrape juice is a liquid. A liquid takes the shape of any container it is in. If you pour grape juice into a different container, the grape juice will take the shape of that container. But the grape juice will still take up the same amount of space.\nA screwdriver is a solid. A solid has a size and shape of its own. This screwdriver has a metal blade and a plastic handle. Both metal and plastic are solids.\nA hammer is a solid. A solid has a size and shape of its own. A hammer is made of iron and wood. Both iron and wood are solids.",
        "split": "test"
    },
    "20231": {
        "question": "Complete the sentence.\nKnitting yarn into a scarf is a ().",
        "choices": [
            "chemical change",
            "physical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade5",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. For example, water vaporizing is a physical change. Liquid water and water vapor are made of the same type of matter: water.",
        "solution": "Knitting yarn into a scarf is a physical change. The yarn gets a different shape, but it is still made of the same type of matter.",
        "split": "test"
    },
    "20382": {
        "question": "What do these two changes have in common?\nbreaking a plate\ncutting your fingernails",
        "choices": [
            "Both are chemical changes.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are caused by cooling."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBreaking a plate is a physical change. The plate gets broken into pieces. But each piece is still made of the same type of matter.\nCutting your fingernails is a physical change. Your fingernails are shorter after you cut them. But the pieces are still made of the same type of matter as the uncut fingernails.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "20384": {
        "question": "Which object has the most thermal energy?",
        "choices": [
            "a fish tank at a temperature of 76°F",
            "a fish tank at a temperature of 52°F",
            "a fish tank at a temperature of 66°F"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter move faster, the temperature goes up. The matter now has both more thermal energy and a higher temperature.",
        "solution": "All three fish tanks have the same mass but different temperatures. Since the 76°F fish tank is the hottest, it has the most thermal energy.",
        "split": "test"
    },
    "20505": {
        "question": "What do these two changes have in common?\nsawing a log in half\nstretching a rubber band",
        "choices": [
            "Both are caused by cooling.",
            "Both are only physical changes.",
            "Both are caused by heating.",
            "Both are chemical changes."
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nSawing a log in half is a physical change. The log splits into two pieces. But the pieces are still made of the same type of matter.\nStretching a rubber band is a physical change. The rubber band gets longer. But it is still made of the same type of matter as before.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are physical changes. No new matter is created.\nBoth are chemical changes.\nBoth changes are physical changes. They are not chemical changes.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "20742": {
        "question": "Which object has less thermal energy?",
        "choices": [
            "a 125-gram glass of grape juice at a temperature of 15°C",
            "a 125-gram glass of grape juice at a temperature of 25°C"
        ],
        "answer": 0,
        "hint": "The objects are identical except for their temperatures.",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Heat and thermal energy",
        "skill": "How is temperature related to thermal energy?",
        "lecture": "All solids, liquids, and gases are made of matter. Matter is made up of tiny particles that are always moving. The energy from the motion of these particles is called thermal energy.\nTemperature measures how hot or cold matter is. If the particles in matter slow down, the temperature goes down. The matter now has both less thermal energy and a lower temperature.",
        "solution": "The two glasses of grape juice have the same mass but different temperatures. Since the 15°C glass of grape juice is colder than the 25°C glass of grape juice, it has less thermal energy.",
        "split": "test"
    },
    "20815": {
        "question": "What do these two changes have in common?\nphotosynthesis\na penny tarnishing",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are chemical changes.",
            "Both are only physical changes."
        ],
        "answer": 2,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade8",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Chemical reactions",
        "skill": "Compare physical and chemical changes",
        "lecture": "Matter is made of very small particles called atoms. Atoms can be linked together by chemical bonds. When two or more atoms link together, they form a molecule.\nIn a chemical change, the chemical bonds in the molecules break. The atoms then link together to form different molecules. The types of molecules in matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then link together in a different way to form different molecules. For example, carbon dioxide molecules are formed when paper burns.\nIn a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, water vaporizing is a physical change that can be caused by heating. Liquid water and water vapor are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nPhotosynthesis is a chemical change. Plants make sugar using carbon dioxide, water, and energy from sunlight.\nMetal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nNeither change is caused by heating.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    },
    "20915": {
        "question": "Complete the sentence.\nGrilling a hamburger is a ().",
        "choices": [
            "physical change",
            "chemical change"
        ],
        "answer": 1,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade4",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Identify physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nBurning a piece of paper is a chemical change. When paper gets hot enough, it reacts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nCutting a piece of paper is a physical change. The cut pieces are still made of paper.\nA change of state is a type of physical change. For example, ice melting is a physical change. Ice and liquid water are made of the same type of matter: water.",
        "solution": "Grilling a hamburger is a chemical change. Heat from the grill causes the matter in the meat to change. Cooked meat and raw meat are different types of matter.",
        "split": "test"
    },
    "21001": {
        "question": "Which would stretch more?",
        "choices": [
            "nylon shorts",
            "glass bowl"
        ],
        "answer": 0,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "physics",
        "category": "Materials",
        "skill": "Compare properties of materials",
        "lecture": "Every object is made of one or more materials. A material is a type of matter. Wood, glass, metal, and plastic are common materials.\nA material has different properties. A material's properties tell you how it looks, feels, tastes, or smells. Some examples of properties are shiny, hard, fragile, and stretchy.\nFor example, a shiny material reflects a lot of light. A fragile material breaks when you drop it.",
        "solution": "Stretchy is a property. A stretchy material gets longer when you pull on it.\nLook at each picture, one at a time. Imagine pulling on the material shown in each picture.\nOf the choices, the nylon shorts would stretch more. If you pull the leg opening on a pair of nylon shorts, it will get wider.",
        "split": "test"
    },
    "21146": {
        "question": "What do these two changes have in common?\nbaking cookies\nrust forming on a metal gate",
        "choices": [
            "Both are caused by cooling.",
            "Both are caused by heating.",
            "Both are only physical changes.",
            "Both are chemical changes."
        ],
        "answer": 3,
        "hint": "",
        "image": null,
        "task": "closed choice",
        "grade": "grade3",
        "subject": "natural science",
        "topic": "chemistry",
        "category": "Physical and chemical change",
        "skill": "Compare physical and chemical changes",
        "lecture": "Chemical changes and physical changes are two common ways matter can change.\nIn a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.\nSome chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.\nIn a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.\nA change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.\nThe law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.",
        "solution": "Step 1: Think about each change.\nBaking cookies is a chemical change. Cookies are made from cookie dough. Baking turns the cookie dough into cookies. The cookies are a different type of matter than the dough.\nRust forming on a metal gate is a chemical change. As the gate rusts, the metal turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.\nStep 2: Look at each answer choice.\nBoth are only physical changes.\nBoth changes are chemical changes. They are not physical changes.\nBoth are chemical changes.\nBoth changes are chemical changes. The type of matter before and after each change is different.\nBoth are caused by heating.\nBaking is caused by heating. But rust forming on a metal gate is not.\nBoth are caused by cooling.\nNeither change is caused by cooling.",
        "split": "test"
    }
}