Question

Strong reducing behaviour ${H_3}P{O_2}$ is due to:
A.One $P - OH$bond
B.One $P - H$bond
C.Two $P - H$bonds
D.Two $P - OH$bonds

Answer 1

To answer this question, you should recall the reducing nature of chemical compounds. Make sure you remember the structures and properties of various acids formed by phosphorus as well as the factors affecting the reducing nature and acidic strength of those acids. A compound is regarded as a reducing agent only if it oxidizes itself while reducing the other reactant.

Complete step by step answer:
Oxoacids refers to the acids that contain the element oxygen. As such, Phosphorus is known to form a large number of oxoacids. Due to its valency phosphorus, it is tetrahedrally surrounded by other atoms. Generally, all these acids are known to form at least one $P = O$ bond and one $P-OH$ bond. $P-P$ or $P-H$ bonds are also found in addition to $P = O$ bonds and $P-OH$ bonds in oxoacids of phosphorus where the oxidation state of phosphorus is less than $+ 5$.
The $P-H$ bonds in oxoacids cannot go through ionization to give ${H^ + }\;$ions whereas the H atoms which are attached with oxygen in $P-OH$ the form are ionizable.
Hence, we can say that only the H atoms attached with oxygen cause basicity. As a result, phosphorous acid ${H_3}P{O_3}$ is dibasic due to the presence of two $P-OH$bonds whereas phosphoric acid ${H_3}P{O_4}$ is tribasic due to the presence of three $P-OH$ bonds.
Oxoacids of phosphorus having $P-H$ bonds have strong reducing properties. For instance: hypophosphorous acid containing two $P-H$ bonds acts as a good reducing agent.
Strong reducing behaviour ${H_3}P{O_2}\;$ is due to the presence of one $- {\text{ }}OH$ group and two $P-H$ bonds.
It has a high tendency to release protons. Thus, exhibits reducing nature.

Hence, the correct option is C.

Note:
Other oxoacids of phosphorus:
Phosphorus acid, ${H_3}P{O_3}$: Phosphorous acid is a diprotic acid that is, it ionizes two protons. It is prepared by hydrolysis of phosphorus trichloride with acid or steam. $PC{l_3}\; + \;3\;{H_2}O\; \to \;HPO{(OH)_2}\; + \;3\;HCl$
Phosphoric acid, ${H_3}P{O_4}$: Phosphoric acid is a triprotic acid that is, it ionizes three protons. It is a non-toxic acid, when pure and is solid at room temperature and pressure. It is prepared by addition of sulphuric acid to tricalcium phosphate rock: $C{a_5}{(P{O_4})_3}X\; + \;5\;{H_2}S{O_4}\; + \;10\;{H_2}O\; \to \;3{H_3}P{O_4}\; + \;5\;CaS{O_4}.2{H_2}O\; + \;HX$