In which of the following reactions ${\mathrm{H}}_2{\mathrm{O}}_2$ acts as a reducing agent? 

(1) ${\mathrm{H}}_2{\mathrm{O}}_2+2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2\mathrm{O}$

(2) ${\mathrm{H}}_2{\mathrm{O}}_2-2{\mathrm{e}}^{-}\to {\mathrm{O}}_2+2{\mathrm{H}}^{+}$

(3) ${\mathrm{H}}_2{\mathrm{O}}_2+2{\mathrm{e}}^{-}\to 2{\mathrm{HO}}^{-}$

(4) ${\mathrm{H}}_2{\mathrm{O}}_2+2{\mathrm{OH}}^{-}-2{\mathrm{e}}^{-}\to {\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}$

detailed solution

Correct option is 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) H2O2−1+2H++2e−→2H2O−2In this reaction, H2O2 undergoes reduction as O shows increase in oxidation number. (2) H2O2−1−2e−→O2o+2H+In the reaction, H2O2 undergoes oxidation as it shows O shows increase in oxidation number. Thus, H2O2 acts as a reducing agent. (3) H2O2−1−2e−→2O-2H−In this reaction, H2O2 undergoes reduction. (4) H2O2−1+2OH−−2e−→O20+2H2OIn this reaction, H2O2 undergoes oxidation. Thus, acts as a reducing agent.