Question

rusting is part of corrison then why is difference between rusting and corrison

Answer 1

b/c rusting is for iron and corrison is for all metals

Answer 2

Rusting causes a layer of mettalic oxide of iron to be formed which flakes off from the surface resulting in exposure of inner surface of iron metal to air. Rusting is the contious process of slow oxidation.

Corrosion is the process in which the surface of metal is attacked by air water or moisture but the oxide so formed does not flake off.
After corrosion oxidation stops