c
\(2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{H}_{2}(\mathrm{g})\)

\(E_{H^{+} / H_{2}}=-\frac{0.0591}{2} \log \frac{P_{M_{2}}}{\left[H^{+}\right]^{2}}\)

\(\log \frac{P_{H_{2}}}{\left[H^{+}\right]^{2}}=0,\)\( \frac{P_{H_{2}}}{\left[H^{+}\right]^{2}}=10^{0}=1\)

\(P H_{2}=\left[H^{+}\right]^{2}\)

For pure \(H_{2} O ; H^{+}=10^{-7} M\)

\(P_{H_{2}}=\left(10^{-7}\right)^{2}=10^{-14} \mathrm{atm}\)