Q. Corrosion of iron is essentially an electro chemical phenomenon where the cell reactions are:

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$Fe$ is oxidized to $Fe ^{3+} \& H_2 O$ is reduced to $O ^{22-}$

$Fe$ is oxidized to $Fe^{ 2+}\& H_2 O$ is reduced to $O _{2}-$

$Fe$ is oxidized to $Fe ^{2+}\& H_2 O$ is reduced to $OH$ - ions

$Fe$ is oxidized to $Fe^{3+}\& H_2 O$ is reduced to $O_2$

Solution:

Explanation: The rusting of iron is $Fe \rightleftarrows Fe ^{2+}+2 e ^{-}$(oxidation)
$H _{2} O +1 / 2 O _{2}+2 e ^{-} \rightleftarrows 2 OH ^{-} \text {(reduction) }$

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