Final answer:
Rust is a chemical change that occurs due to a redox reaction when iron is exposed to moisture and oxygen, resulting in the formation of iron (III) oxide, also known as rust.
Step-by-step explanation:
Therefore, rust is a chemical change. Rust formation happens when iron (Fe) is exposed to moisture and oxygen in the environment, leading to a series of redox reactions. This process involves the oxidation of iron to iron (II) ions (Fe2+) and ultimately leads to the formation of iron (III) oxide (Fe2O3), commonly known as rust. The creation of rust signifies a chemical reaction because new substances are formed and the change is not easily reversible. It is part of a broader category of phenomena known as corrosion, which signifies the deterioration of materials through chemical interactions with their environment.