A gate made of painted iron is beginning to rust in areas where the paint has worn away. The paint served as a protective barrier between the iron and the oxygen in the air. Why is the formation of rust considered a chemical process

A. Rust and iron are completely different substances with different properties.

B. Rust is just a different state of matter than iron.

C. Rust is a different color than iron.

D. Rust has the same arrangement and types of atoms as pure iron.