The pressure of H₂ required to make the potential of H₂ electrode zero, in pure water, at 298 K, is

In case of hydrogen electrode,
$2{\mathrm{H}}_{\left(\mathrm{aq}\right)}^{\mathrm{+}}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_{2\left(\mathrm{g}\right)}$
${\mathrm{E}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cell}}^{\mathrm{0}}-\frac{0.059}{\mathrm{n}}\log \hspace{0.17em}\mathrm{k}$
$\mathrm{0}=0-\frac{0.059}{\mathrm{2}}\log \mathrm{\hspace{0.17em}}\frac{{\mathrm{P}}_{{\mathrm{H}}_{\mathrm{2}}}}{{\left[{\mathrm{H}}^{\mathrm{+}}\right]}^{\mathrm{2}}}$
${\text{P}}_{{\text{H}}_{\text{2}}}={\left[{\text{H}}^{\text{+}}\right]}^2={\left({10}^{-7}\right)}^2$
$(\mathrm{for} \mathrm{water} \left[{\mathrm{H}}^{\mathrm{+}}\right]=\left[{\mathrm{H}}^{-}\right]={10}^{-7}\hspace{0.17em}\mathrm{m}$
${\mathrm{P}}_{{\mathrm{H}}_{\mathrm{2}}}=1\times {10}^{-14}\hspace{0.17em}\mathrm{atm}$