Why HNO₃ is used as oxidizing agent?

Solution:

Nitrogen can have oxidation numbers from −3 to +5. The oxidation number of nitrogen in HNO₃ is +5. Thus, increase in oxidation number beyond +5 cannot occur. Hence, HNO ₃ cannot act as reducing agent. The oxidation number of nitrogen in HNO ₃can only decrease; thus, it acts as an oxidizing agent.