The process of slowly eating away of the metal due to attack of the moisture and atmospheric gases on the surface of the metal resulting into the formation of compound such as oxides, sulphides, carbonates, sulphates etc., is called corrosion.
The electrochemical phenomenon of rusting of iron can be described as :
At Anode: Fe(s) undergoes oxidation to releases electrons.
Electrons released at anode move to another metal and reduce oxygen in presence of H+. It is available from H2CO3 formed from the dissolution of CO2 from air into water. H+ in water may be available also through dissolution of other acidic oxides from the atmosphere.
This site behaves as cathode
