Why does H3PO3 acts as a reducing agent but H3PO4 does not?

H3PO3 contains one P H bond and hence acts as a reducing agent but H3PO4 does.

Related Questions:

Which is more basic N(CH3)3 or N(SiH3)3 , explain?

Are all the five bonds of PCl5 equivalent? Justify your answer.

Trisilyl amine, N(SiH3)3 is planar whereas trimethyl amines N(CH3)3 is pyramidal. Explain why?.

What are common structural features of oxides (P4O6 and P4O5) of phosphorous?

What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

What are abnormal behaviour of Nitrogen atom as compared to other family members?

What is product obtained when N2O5 is treated with NaCl?

What is metaphophoric (HPO3)?

Phosphorus can form PCl5 but nitrogen can not form NCl5 why?

Why PCl3 hydrolysed while NCl3 can not be hydrolysed? 

Why bond angle of hydrides of group 15, decreases down the group?

What is "calgon" ? Give structure and its uses?

Why nitrogen shows catenation properties less than phosphorus?

Why Nitrogen is fairly inert gas?

Why Nitrogen (N2) is less reactive at room temperature?

Why Nitrogen dioxide (NO2) dimerises to form Dinitrogen tetraoxide (N2O4)?

Why Nitrogen dioxide (NO2) is coloured but Dinitrogen tetraoxide (N2O4) is colourless?

Hypophosphorous acid (H3PO2) and Phosphorous acid (H3PO3) act as as good reducing agents while H3PO4 does not.Why?