Which of the following statements about combustion is true?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → It is a chemical process in which a substance reacts with oxygen to give off heat.
Combustion is a chemical process in which a substance reacts with oxygen and gives off heat (often light as well). New substances such as carbon dioxide and water are formed, which is why it is a chemical change.
Why the other options are incorrect
Option (1) It is a physical process in which a substance reacts with oxygen to give off heat. — Incorrect. Burning forms new substances, so it is a chemical process, not a physical one.
Option (2) It is a chemical process in which a substance reacts with nitrogen to give off heat. — Incorrect. Nitrogen does not support burning; oxygen does.
Option (4) It is a chemical process in which a substance reacts with carbon dioxide to give off heat. — Incorrect. Carbon dioxide is a product of burning and is used to put out fires.