Which of the following is not a chemical change?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Beating aluminium to make aluminium foil
In a chemical change new substances are formed; in a physical change only the shape, size or state changes. Beating aluminium into foil changes only its shape; the foil is still aluminium, so this is a physical change.
Why the other options are incorrect
Option (1) Photosynthesis — Incorrect. Plants turn carbon dioxide and water into glucose and oxygen, which are new substances.
Option (2) Digestion of food — Incorrect. Enzymes break food down into simpler new substances such as glucose and amino acids.
Option (3) Burning of coal — Incorrect. Coal reacts with oxygen to form carbon dioxide, giving out heat.