Question

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. Why ?

Answer 1

The S atom in $S{O}_2$ has +4 oxidation number. The minimum and maximum oxidation numbers of S are -2 and +6 respectively. Hence, in $S{O}_2$, S can increase and decrease its oxidation number. Hence, $S{O}_2$ is an oxidizing agent as well as reducing agent.
The O atom in hydrogen peroxide has oxidation number of -1. The minimum and maximum oxidation numbers of O are -2 and 0 respectively. Hence, hydrogen peroxide is oxidant as well as reluctant.
In ozone, O atom has oxidation number of 0. It can decrease its oxidation number to -1 or -2 but cannot increase it. Hence ozone is an oxidizing agent.
In nitric acid, N has oxidation number of +5 which is maximum. N can only decrease its oxidation number. Hence, nitric acid is an oxidizing agent.