Question

Strong reducing behaviour of `H_(3)PO_(4)` is due to :
A. High oxidation state of phosphorus
B. Presence of two`-OH` group and one `P-H` bond
C. Presence of one `-OH` group and two `P-H` bond
D. High electron gain enthalpy of phosphorus

Answer 1

Correct Answer - 3
Acids which contain `P-H` bond have strong reducing properties .For example ,hypophosphorous acid `(H_(3)PO_(2))` is a good reducing agent as it contains two `P-H` bonds and thus reduces `AgNO_(3)` to metallic `Ag` and `HgCl_(2)` to `Hg`
`4AgNO_(3)+H_(3)PO_(2)+2H_(2)Orarr4Agdownarrow+H_(3)PO_(4)+4HNO_(3)`
`2HgCl_(2)+H_(3)PO_(2)+2H_(2)Orarr2Hg+H_(3)PO_(4)+4HCl`
ti also reduces arenediazonium sales to arenes:
`2C_(6)H_(5)N_(2)Cl+H_(3)PO_(2)+2H_(2)Orarr2C_(6)H_(6)+H_(3)PO_(4)+2N_(2)+2HCl`