Physical and chemical changes Quiz - ICSE Class 7 Science
Free practice quiz: Physical and chemical changes (ICSE Class 7 Science). 46 multiple-choice questions with answers and explanations. Play online, no sign-up needed.
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Which of the following is an example of a reversible physical change?
- Burning of wood
- Rusting of iron
- Melting of ice
- Digesting food
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Answer: C. Melting of ice
Melting of ice is a physical change because only the state of matter changes (solid to liquid), and it can be reversed by freezing. Burning wood, rusting iron, and digesting food are chemical changes as new substances are formed and they are generally irreversible.
Which of the following is a characteristic of a chemical reaction often observed as a sign of a chemical change?
- Change in size
- Change in shape
- Formation of gas bubbles
- Change in state without heat
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Answer: C. Formation of gas bubbles
Formation of gas bubbles (effervescence) is a common indicator that a new substance (a gas) is being formed, which is characteristic of a chemical change. Changes in size, shape, and state are usually physical changes.
Which of the following is NOT a reversible physical change?
- Stretching a rubber band
- Condensation of steam
- Burning a log of wood
- Dissolving sugar in water
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Answer: C. Burning a log of wood
Burning a log of wood is a chemical change that converts wood into ash, carbon dioxide, and water vapor, which cannot be easily reversed. Stretching a rubber band, condensation of steam, and dissolving sugar are physical changes that are generally reversible.
The process of breaking a stone into smaller pieces is:
- A chemical change because its size changes
- A physical change because its chemical composition is unaltered
- A chemical change because it is irreversible
- A physical change because it is reversible
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Answer: B. A physical change because its chemical composition is unaltered
Breaking a stone changes its size and shape but not the chemical makeup of the stone. Therefore, it's a physical change. While reassembling the stone might be impractical, the nature of the change is physical.
The process of respiration in living organisms is:
- A physical change
- A reversible physical change
- An irreversible chemical change
- A temporary physical change
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Answer: C. An irreversible chemical change
Respiration is a complex series of metabolic chemical reactions that break down glucose in the presence of oxygen to release energy, carbon dioxide, and water. This is a chemical change and is irreversible in the context of the biological process.