In which one of the following cases do both physical and chemical chan

In which one of the following cases do both physical and chemical changes take place?

Burning of candle

Freezing of water

Cooking of food

Rusting of iron

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This question was previously asked in

UPSC CDS-2 – 2023

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A physical change involves a change in the form or appearance of a substance but not its chemical composition (e.g., changes of state). A chemical change involves a change in the chemical composition of a substance, resulting in the formation of new substances (e.g., combustion, rusting).

In the burning of a candle, the wax melts (physical change) and turns into liquid. This liquid wax is then drawn up the wick, vaporizes, and reacts with oxygen in the air (combustion), producing carbon dioxide, water vapor, heat, and light (chemical change). Thus, both physical (melting/vaporization of wax) and chemical (combustion of wax vapor) changes occur simultaneously as the candle burns.

Freezing of water is purely a physical change (liquid to solid). Rusting of iron is a chemical change (iron reacts with oxygen and water). Cooking of food involves primarily chemical changes in the food components (e.g., protein denaturation, starch gelatinization), although physical processes like boiling water might be involved as a heating method.

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