Final answer:
The formation of water (H2O) represents a chemical change because it entails the formation of new chemical bonds between hydrogen and oxygen atoms, resulting in a new substance with different properties.
Step-by-step explanation:
When water (H2O) is formed, a chemical change takes place. This involves a reaction where hydrogen and oxygen atoms bond together to form water molecules. In this process, the properties of the substances change as new chemical bonds are formed, which is a hallmark of a chemical change. Examples of physical changes include boiling or melting, where a substance changes form but not its chemical identity. Meanwhile, a change like the rusting of iron, burning of gasoline, or souring of milk demonstrates a chemical transformation, where the substances involved are converted into entirely new materials with different chemical compositions.