Question

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

Answer 1

Oxidizing agents itself get reduced. Reducing agents itself gets oxidized. Oxidation means increase in oxidation no. while reduction means reduce in oxidation no.

Complete step-by-step answer:
In $S{O_2}$, the oxidation no of $S$ is +4 and the range of O.N. that $S$ can have is from +6 to -2 therefore, $S{O_2}$ can act as an oxidizing as well as reducing agent.
In ${H_2}{O_2}$, the O.N. that $O$ is -1 and the range of the O.N. that $O$ can have is from $O$ to -2 Hence, ${H_2}{O_2}$ can act as oxidizing as well as reducing agent.
In ozone, the O.N. of $O$ is zero and the range of O.N. that $O$ can have is from 0 to -2 therefore, O.N. can only decrease, Hence, $O$ acts as an oxidant.
In $HN{O_3}$, the O.N. of $N$ is +5 and range of O.N. that $N$ can have is from +5 to -3, therefore the O.N. of $N$ can only decrease in this case Hence, $HN{O_3}$ acts only as oxidant.

Additional information : Oxidizing agents have the ability to oxidize other substances, in other words to accept their electrons, common oxidizing agents are oxygen, hydrogen, peroxide and the halogens.
An oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons in that sense it is one component in the oxidation-reduction reaction.
A reducing agent is an element or compound that loses an electron to an electron recipient in a redox chemical reaction. A reducing agent is thus oxidized when it loses electrons in the redox reaction reducing agent reduces oxidizing agents oxidize oxidizes.

Note: Oxygen can sometimes also attain the oxidation numbers +1 to +2.The abbreviation O.N. refers to oxidation number.