Which of the following chemical reactions are involved in the corrosion of iron metal?

Corrosion is defined as the oxidation of metals that are exposed for longer periods to air and water. It is the process of gradual degradation of metallic surfaces by air or moisture.
Metals like iron, silver, and copper get corroded readily and lead to the deposition of coloured metal oxides on the surfaces. Corrosion of iron is specifically termed rusting. In rusting, the iron metal gets oxidized to iron oxide leading to the deposition of brownish-red iron oxide powder called rust on metal surfaces.
 

The reaction involved is-
4Fe + 3O₂ + 2xH₂O $\to$ 2Fe₂O₃.xH₂O (Rust)
 

The chemical reaction involved in the corrosion of iron metal is that of oxidation as well as combination.