Sulphur dioxide and hydrogen peroxide can act as both oxidizing and reducing agents in their reactions,while ozone and nitric acid act only as oxidants. Why?

(N/A) $SO_{2}$: In $SO_{2}$,the oxidation number of $S$ is $+4$. The oxidation number of $S$ ranges from $-2$ to $+6$. Therefore,the oxidation number of $S$ in $SO_{2}$ can both increase and decrease,allowing it to act as either an oxidizing or a reducing agent.
$(b)$ $H_{2}O_{2}$: In $H_{2}O_{2}$,the oxidation number of $O$ is $-1$. The oxidation number of oxygen can increase to $0$ (in $O_{2}$) or decrease to $-2$ (in $H_{2}O$ or $OH^-$). Thus,$H_{2}O_{2}$ can act as both an oxidizing and a reducing agent.
$(c)$ $O_{3}$: The oxidation number of oxygen in $O_{3}$ is $0$. It can only be reduced to $-1$ or $-2$. Therefore,it acts only as an oxidizing agent.
$(d)$ $HNO_{3}$: The oxidation number of nitrogen in $HNO_{3}$ is $+5$,which is its maximum oxidation state. Therefore,it can only be reduced,meaning $HNO_{3}$ acts only as an oxidizing agent.