Which process is a physical change? iron rusting milk turning into curd water boiling paper burning hard water stains pipes?

Option (c) is the correct answer.

Explanation:

A change that causes no change in chemical composition of a substance is known as a physical change.

For example, boiling of water is a physical change as state of water is changing from liquid to vapors.

On the other hand, a change that causes a change in chemical composition of a substance is known as a chemical change.

For example, rusting of iron, churning of milk into curd, burning of paper, stains of hard water on pipes are all chemical changes.

Thus, we can conclude that water boiling process is a physical change.