Which statement about a chemical reaction is true? it occurs only at low temperatures. it occurs only at high temperatures. it occurs whenever a physical change takes place. it occurs whenever a chemical change takes place.

Option (d) is the correct answer.

Explanation:

A reaction which causes a change in the rearrangement of atoms or chemical composition of a substance is known as a chemical change.

A chemical change can take place rapidly, slowly or too slowly.

For example, rusting of iron is a slow chemical change.

Therefore, the statement which is true about a chemical reaction is that it occurs whenever a chemical change takes place.

The correct statement is it occurs whenever a chemical change takes place.

Explanation:

A physical reaction is defined as the reaction in which a change in shape, size takes place. No new substance gets formed in these reactions.

A chemical reaction is defined as the reaction in which a change in chemical composition takes place. A new substance is formed in these reactions.

These reactions can happen at any temperature. Like in cold conditions, Azo dye is prepared and at high temperatures, dissociation of water takes place.

Thus, a chemical reaction occurs only when a chemical change takes place in a substance.

Hence, the correct statement is it occurs whenever a chemical change takes place.

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