In which of the following reactions $\mathrm{H}_{2} \mathrm{O}_{2}$ acts as a reducing agent? (a) $\mathrm{H}_{2} \mathrm{O}_{2}+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}$ (b) $\mathrm{H}_{2} \mathrm{O}_{2}-2 \mathrm{e}^{-} \longrightarrow \mathrm{O}_{2}+2 \mathrm{H}^{+}$ (c) $\mathrm{H}_{2} \mathrm{O}_{2}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{OH}^{-}$ (d) $\mathrm{H}_{2} \mathrm{O}_{2}+2 \mathrm{OH}^{-}-2 \mathrm{e}^{-} \longrightarrow \mathrm{O}_{2}+2 \mathrm{H}_{2} \mathrm{O}$

JEE Main · 2014 · 06 Apr 2014 · Offline · Hydrogen

In which of the following reactions

H_{2} O_{2}

acts as a reducing agent?
(a)

H_{2} O_{2} + 2 H^{+} + 2 e^{-} ⟶ 2 H_{2} O

(b)

H_{2} O_{2} - 2 e^{-} ⟶ O_{2} + 2 H^{+}

(c)

H_{2} O_{2} + 2 e^{-} ⟶ 2 OH^{-}

(d)

H_{2} O_{2} + 2 OH^{-} - 2 e^{-} ⟶ O_{2} + 2 H_{2} O

Answer: (B)

A reducing agent is the species that loses electrons, that is, is itself oxidised. In the two half-reactions where

H X_{2} O X_{2}

appears on the left losing electrons and turning into

O X_{2}

, namely (b) and (d), hydrogen peroxide is the reducing agent. In (a) and (c) it gains electrons and so acts as an oxidising agent instead. So

H X_{2} O X_{2}

is the reducing agent in (b) and (d).

JEE Main · 2014 · 06 Apr 2014 · Offline · Single correct option