Give reasons:
`H_(3)PO_(3)` undergoes disproportionation reaction, but `H_(3)PO_(4)` does not.

Explanation

In disproportionation reactions simultaneous oxidation and reduction of an element take place. In `H_(3)PO_(3)` phosphorus shows +3 oxidation state due to which it can be easily disproportionate to `PH_(3)` (with -3 oxidation state) and `H_(3)PO_(4)` (with +5 oxidation state). The +5 oxidation state is the highest oxidation state of phosphorus in its compounds. Thus, further oxidation of `H_(3)PO_(4)` is not possible. Hence, it cannot undergo disproportionation reaction.