Explain how rusting of iron is envisaged as setting up of an electroCHMemical cell.

Explanation

Formation of carbonic acid takes place on the surface of iron:
`H_(2)O(l)+CO_(2)(g)rarrH_(2)CO_(3)hArr2H^(+)+CO_(3)^(2-)`
In presence of `H^(+)` ion, oxidation of iron takes place
`Fe(s)rarrFe^(2+)(aq)+2e^(-)`
The electrons are used at other spot where reduction takes place:
`O_(2)(g)+4H^(+)(aq)=4e^(-)rarr2H_(2)O(l)`
Overall reaction is:
`2Fe(s)+O_(2)(g)+4H^(+)(aq)hArr2Fe^(2+)(aq)+2H_(2)O(l)`
Thus, an electrochemical cell is established on the surface.