Final answer:
The rusting of iron is a chemical change because it results in the formation of a new substance, iron oxide, through a reaction with oxygen, and does not simply involve a change in the appearance or state of iron.
Step-by-step explanation:
The rusting of a piece of iron under environmental conditions is not a physical change; it is a chemical change. This is because iron undergoes a chemical reaction with oxygen, resulting in a new substance, iron oxide or rust. The process is also known as corrosion and is an example of a redox reaction where iron is first oxidized to iron (II) ions, and then these ions are further oxidized, combining with water and oxygen gas to produce rust. Physical changes involve changes in the state or appearance of a substance without altering its composition, such as melting or boiling. Since the iron is being chemically altered to create a new substance, iron oxide, rusting does not fit this description.