Rusting is a :a.) chemical changeb.) physical changec.) can’t be saidd.) both

Rusting is a chemical change.

Explanation:
Rusting occurs when iron reacts with oxygen and moisture (water) in the environment to form iron oxide (Fe₂O₃·nH₂O), commonly known as rust. This process alters the chemical composition of iron, transforming it into a different substance (iron oxide), which is irreversible under normal conditions.

Chemical change: In a chemical change, a new substance is formed, and the change is generally not reversible. Rusting fits this definition because the iron metal changes to iron oxide, a different compound.
Physical change: A physical change involves a change in the physical state or appearance of a substance without altering its chemical composition. Rusting is not a physical change, as the substance's chemical structure is modified.
Therefore, the correct answer is (a) chemical change.