What happens to the molecules of a substance during a chemical change ? 1. The molecules in the substance get larger or smaller.

2. During a chemical change, the substances molecules stay the same.

3. Some molecules melt when they are combined with other molecules.

4.Bonds in the molecules are made or broken to a form new molecules.

Option 4 - Bonds in the molecules are made or broken to form new molecules.

Explanation:

In chemical changes, new substances are formed and the process is often difficult to reverse. During chemical changes, particles do change with atoms or ions regrouping. Bonds (links) between atoms break and new ones form and energy are either given out or taken in. Some chemical changes are initiated by mixing.

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c- cold periods in earth's history during which glaciers covered much of the surface.

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