Question

Which one of the following anions can undergo both oxidation and reduction?

• A. $C{r}_2{O_7}^{2-}$
• B. $N{O_3}^{-}$
• C. $OC{l}^{-}$
• D. $S^{2-}$

Answer 1

The correct option is C $OC{l}^{-}$

$\left(A\right)$ In $C{r}_2{O_7}^{2-}$, the oxidation state of $Cr$ is $+6$, which is maximum oxidation of $Cr$. It can only lower down its oxidation state. So, it acts only as an oxidising agent.
$\left(B\right)$ In $N{O_3}^{-}$, the oxidation state of $N$ is $+5$, which is the maximum oxidation of $N$. It can only lower its oxidation state and so, it acts only as an oxidising agent.
$\left(C\right)$ In $OC{l}^{-}$, the oxidation state of $Cl$ is $+1$ and $Cl$ shows oxidation state from $-1$ to $+7$ and so, it can undergo both oxidation and reduction.
$\left(D\right)$ In $S^{2-}$, the oxidation state of $S$ is $-2$, which is the minimum oxidation state of $S$ and so, it can only increase its oxidation state and hence, it acts only as a reducing agent.

Therefore, $OC{l}^{-}$ can undergo both oxidation as well as reduction.