Which of the following is an example of a physical change?

• A. Rust forming on iron
• B. Burning wood to ash
• C. Melting ice into water
• D. Digestion of food

Answer: (C)

Melting ice into water is an example of a physical change because it involves a transition from one state of matter (solid) to another (liquid) without altering the chemical composition of the substance. When ice melts, the water molecules are still present and retain their chemical identity as H₂O; they simply move from a structured, rigid arrangement (solid) to a more loosely connected arrangement (liquid) due to the increase in temperature.

In contrast, the other processes listed involve chemical changes, where the substances undergo transformation into different chemical entities. Rust forming on iron involves a reaction with oxygen, producing iron oxide, which is a new substance. Burning wood results in combustion that transforms wood's organic compounds into ash, carbon dioxide, and other products, indicating a chemical change. Digestion of food breaks down complex molecules into simpler ones through reactions that change the original compounds into different substances, a hallmark of chemical processes.