`HNO_(3)` is an oxidising agent but `H_(3)PO_(4)` is not. Explain. 

Explanation

The inability of nitrogen atom to unpair and promote its 2s-electron results in the pentapositive state of nitrogen being less stable than tripositive. Thus, `HNO_(3)` where nitrogen is in `+5` oxidation state is an oxidizing agent. On the other hand P has d-orbitals to expand its octet and also shows no inert pair effect, is quite stable in V state. Thus, `H_(3)PO_(4)` in which Pis in `+5` oxidation tate is not oxidizing.