Which of the following species can act as both an oxidizing and a reducing agent?

Solution

1. In ${\text{H}}_2{\text{O}}_2$, oxygen is in $-1$ state, which can go to $0$ (oxidation) or $-2$ (reduction).
2. In ${\text{SO}}_2$, sulfur is in $+4$ state, which can go to $+6$ (oxidation) or $0$ or $-2$ (reduction).
3. ${\text{KMnO}}_4$ only acts as an oxidizing agent because Mn is in its highest oxidation state of $+7$.
4. Both ${\text{H}}_2{\text{O}}_2$ and ${\text{SO}}_2$ can function as both agents.
5. Hence the answer is (D).