Rusting is an electrochemical phenomenon occurring in the presence of water and oxygen.

• Mechanism:

1. Anodic region: Iron is oxidized to ferrous ions. $2Fe(s)\to 2F{e}^{2+}+4e^{-}$ (Oxidation)
2. Cathodic region: Oxygen is reduced in the presence of $H^{+}$ (from $C{O}_2+H_{2}O\to H_{2}C{O}_3$). $O_2(g)+4H^{+}+4e^{-}\to 2H_{2}O(l)$ (Reduction)

• The ferrous ions are further oxidized by atmospheric oxygen to form hydrated ferric oxide ($F{e}_2{O}_3\cdot x{H}_{2}O$), which is Rust. Since both oxidation and reduction occur, it is a Redox Reaction.