Question

In which of the following reactions $H_{2}O_{2}$ acts as a reducing agent?
(1) $H_{2}O_{2} + 2H^{+} + 2e^{-} \to 2H_{2}O$
(2) $H_{2}O_{2}- 2e^{-} \to O_{2} + 2H^{+}$
(3) $H_{2}O_{2} + 2e^{-} \to 2HO^{-}$
(4) $H_{2}O_{2} + 2OH^{-} -2e^{-} \to O_{2} + 2H_{2}O$

• A. $1,2$
• B. $3, 4$
• C. $1,3$
• D. $2,4$

Answer 1

Answer: (D)

The reducing agent oxidises itself by undergoing oxidation through the loss of electrons. Thus, reducing agent reduces other molecules by supplying electrons to them.
$(1) H_{2}O_{2}^{-1} + 2H^{+} + 2e^{-} \to 2H_{2}O_{2}$
In this reaction, $H_2O_2$ undergoes reduction as $O$ shows increase in oxidation number.
$(2) H_{2}O_{2}^{-1} -2e^{-} \to O^{o}_{2} + 2H^{+}$
In this reaction, $H_2O_2$ undergoes oxidation as it shows decrease in oxidation number. Thus, $H_{2}O_{2}$ acts as a reducing agent.
$(3) H_{2}O_{2}^{-1} -2e^{-} \to 2O^{-2}H^{-}$
In this reaction, $H_{2}O_{2}$ undergoes reduction.
$(4) H_{2}O_{2}^{-1} - 2OH^{-} - 2e^{-} \to O^{o}_{2} + 2H_{2}0$
In this reaction, $H_{2}O_{2}$ undergoes reduction. Thus, acts as a reducing agent.