The reaction occurring at the cathode of miniature electrochemical cell during the rusting of iron is

The reaction occurring at the cathode of miniature electrochemical cell during the rusting of iron is ${\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}+2{\mathrm{e}}^{-}⟶2{\mathrm{OH}}^{-}$.

An oxidation process is rusting. Rust is created when iron combines with oxygen and water to generate hydrated iron(III) oxide. Steel and iron rust when they come into contact with oxygen and water, which are both necessary for rusting to take place.

Hence, correct option is C.