Select ALL species that can act both as an oxidising agent and as a reducing agent (judge by the oxidation state of the non-hydrogen element, in suitable reactions).

A species can do both if its element is in an intermediate oxidation state. S in $\mathrm{SO}{}_2$ is +4 (range -2 to +6), O in $\mathrm{H}{}_2\mathrm{O}{}_2$ is -1 (range -2 to 0), and N in $\mathrm{HNO}{}_2$ is +3 (range -3 to +5). N in $\mathrm{HNO}{}_3$ is +5, the maximum, so it can only oxidise.