What happens when H3PO3 is heated

What happens when H₃PO₃ is heated?
Answer

H₃PO₃, on heating, undergoes disproportionation reaction to form PH₃ and H₃PO₄. The oxidation numbers of P in H₃PO₃, PH₃, and H₃PO₄ are +3, −3, and +5 respectively. As the oxidation number of the same element is decreasing and increasing during a particular reaction, the reaction is a disproportionation reaction.