Which of the following reactions is used to make a fuel cell?

• A

  $\begin{aligned} & \mathrm{Cd}_{(s)}+2 \mathrm{Ni}(\mathrm{OH})_{3(s)} \\ & \rightarrow \mathrm{CdO}_{(s)}+2 \mathrm{Ni}(\mathrm{OH})_{2(s)}+\mathrm{H}_2 \mathrm{O}_{(l)}\end{aligned}$
• B

  $\mathrm{Pb}_{(s)}+\mathrm{PbO}_{2(s)}+2 \mathrm{H}_2 \mathrm{SO}_{4(a q)}$ $\rightarrow 2 \mathrm{PbSO}_{4(s)}+2 \mathrm{H}_2 \mathrm{O}_{(l)}$
• Correct answer
  C

  $2 \mathrm{H}_{2(\mathrm{~g})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{H}_2 \mathrm{O}(l)$
• D

  $2 \mathrm{Fe}_{(s)}+\mathrm{O}_{2(g)}+4 \mathrm{H}^{+}{ }_{(a q)} \rightarrow 2 \mathrm{Fe}^{2+}{ }_{(a q)}+2 \mathrm{H}_2 \mathrm{O}_{(l)}$

Hence, the correct answer is option: 'C'.