Question

Hydrogen peroxide acts both as an oxidising and as a reducing agent depending upon the nature of the reacting species. In which of the following cases $H_2{O}_2$ acts as a most suitable reducing agent in acid medium ?

• A. KI
• B. ${\text{Cr}}_2{\text{O}}_7^{2-}$
• C. $\text{S}{\text{O}}_3^{2-}$
• D. $\text{Mn}{\text{O}}_4^{-}$

Answer 1

Answer: (D)

$Mn{O}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O$
$H_2{O}_2\to O_2+2H^{+}+2e^{-}$
$H_2{O}_2$ acts as reducing agent gets oxidised
$H_2{O}_2\stackrel{K_{2}C{r}_2{O}_7}{\to }Cr{O}_5$
$Cr{O}_5$ formation possibility is there, so $K_{2}C{r}_2{O}_7$ not selected as choice but $KMn{O}_4$ selected.