Question

The compound that cannot act both as oxidising and reducing agent is:

• A. $H_{3}P{O}_4$
• B. $HN{O}_2$
• C. $H_{2}S{O}_3$
• D. $H_2{O}_2$

Answer 1

The correct option is A $H_{3}P{O}_4$

A reducing agent is that which can release electrons.

An oxidizing agent is that which can accept electrons easily.

Oxidation number of $P$ in $H_{3}P{O}_4$:

$3(+1)+x+4(-2)=0$
$3+x-8=0$
$x=+5$

Here, $P$ has its highest oxidation state $+5$ implying that it cannot further release more electrons to act as a reducing agent. Therefore, $H_{3}P{O}_4$ can act only as an oxidizing agent.