Which of the following reactions involves disproportionation?

Solution

1. Identify the oxidation state of chlorine in ${\text{Cl}}_2$, which is $0$.
2. In the product ${\text{Cl}}^{-}$, the oxidation state of chlorine is $-1$ (reduction).
3. In the product ${\text{ClO}}^{-}$, the oxidation state of chlorine is $+1$ (oxidation).
4. Since chlorine is both oxidized and reduced, this is a disproportionation reaction.
5. Hence the answer is (B).