Question

Which of the following phosphorus oxyacids can act as reducing agent?

• A. $H_{3}P{O}_3$
• B. $H_{3}P{O}_4$
• C. $H_2{P}_2{O}_6$
• D. $H_4{P}_2{O}_7$

Answer 1

Answer: (A)

$H_{3}P{O}_3$

Phosphorous acid $H_{3}P{O}_3$ is a strong reducing agent. Thus it reduces silver nitrate to metallic silver, gold trichloride to metallic gold, mercuric chloride to mercurous chloride and copper sulphate to metallic copper.

$2AgN{O}_3+H_{3}P{O}_3+H_{2}O\to 2Ag\downarrow +2HN{O}_3+H_{3}P{O}_4$

Phosphorous acid itself gets oxidized to phosphoric acid $H_{3}P{O}_4$

So, the correct option is $A$