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 $H_2O_2$ 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)

$ MnO _4^{-}+8 H ^{+}+5 e ^{-} \rightarrow Mn ^{2+}+4 H _2 O $
$ H _2 O _2 \rightarrow O _2+2 H ^{+}+2 e ^{-}$
$H _2 O _2$ acts as reducing agent gets oxidised
$H _2 O _2 \xrightarrow{ K _2 Cr _2 O _7} CrO _5$
$CrO _5$ formation possibility is there, so $K _2 Cr _2 O _7$ not selected as choice but $KMnO _4$ selected.