Among the following oxoacids of phosphorus, the strongest reducing property is for:

The reducing property of oxoacids of phosphorus is due to the presence of $\text{P-H}$ bonds. The more $\text{P-H}$ bonds present, the stronger the reducing power.${\text{H}}_3{\text{PO}}_4$: No $\text{P-H}$ bonds.${\text{H}}_3{\text{PO}}_3$ (Phosphorous acid): One $\text{P-H}$ bond.${\text{H}}_3{\text{PO}}_2$ (Hypophosphorous acid): Two $\text{P-H}$ bonds.Therefore, ${\text{H}}_3{\text{PO}}_2$ is the strongest reducing agent.