Give reasons H3PO3 undergoes disproportionation reaction but H3PO4 does not.

The oxidation number of P in H3PO3 and H3PO4 is +3 and +5 respectively. H3PO4 can only undergo reduction as the maximum possible oxidation state for P is +5. H3PO3 can undergo oxidation as well as reduction. Hence, H3PO3 undergoes disproportionation reaction but H3PO4 does not. Note: Disproportionation reaction of H3PO3. 4H3PO3 Δ → 3H3PO4 + PH3