Question

H3PO2 is a stronger reducing agent than H3PO3. why?

Answer 1

Reducing agents are those molecules which can donate electrons...

In $H_3PO_2$ & $H_3PO_3$ the donating elctrons are Hydrogen atoms which are bonded to phosphorus atom

In case of $H_3PO_2$ there are two hydrogen bonded to P atom
But in case of $H_3PO_3$ there are only one hydrogen bonded to P atom

Therefore $H_3PO_2$ has more donating electrons than $H_3PO_3$.

Therefore $H_3PO_2$ is stronger reducing agent than $H_3PO_3$.

Answer 2

Hey !!

In H₃PO₂, oxidation state of P is +1 which can be further oxidized to a higher oxidation state. While in H₃PO₄, oxidation state of P is +5, which is highest for P. It cannot be further oxidized. Hence, H₃PO₄ is a weaker reducing agent.

Good luck !!