Strong reducing behaviour of H3PO2 is due to
High electron gain enthalpy of phosphorus
High oxidation state of phosphorus
Presence of two -OH groups and one P - H bond
Presence of one - OH group and P - H bonds.
All oxyacids of phosphorus which have P - H bonds act as strong reducing agents. H3PO2 has two P - H bonds hence, it acts as a strong reducing aqent.