$\mathrm{H}_{2} \mathrm{O}_{2}$ acts as a reducing agent in :

1. A $$\mathrm{Mn}^{2+}+2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{MnO}_{2}+2 \mathrm{H}_{2} \mathrm{O}$$
2. B $$2 \mathrm{Fe}^{2+}+2 \mathrm{H}^{+}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{Fe}^{3+}+2 \mathrm{H}_{2} \mathrm{O}$$
3. C $$\mathrm{Na}_{2} \mathrm{S}+4 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+4 \mathrm{H}_{2} \mathrm{O}$$
4. D $$2 \mathrm{NaOCl}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}$$ Correct answer