Oxidation potential of hydrogen electrode is highest when it is in contact with a solution of

$$\begin{gathered} {\mathrm{E}}_{{\mathrm{RP}}^{ }}=-0.0591\times {\mathrm{p}}^{\mathrm{H}}; \\ \mathrm{As} {\mathrm{p}}^{\mathrm{H}} \mathrm{increases}, \mathrm{reduction} \mathrm{potential} \mathrm{decreases}; \\ {\mathrm{E}}_{\mathrm{RP}}\propto \left[{\mathrm{H}}^{+}\right] , {\mathrm{E}}_{\mathrm{RP}}=-{\mathrm{E}}_{\mathrm{OP}} ; \\ \mathrm{Lesser} \mathrm{the} \mathrm{reduction} \mathrm{potential}, \mathrm{higher} \mathrm{the} \mathrm{oxidation} \mathrm{potential}. \end{gathered}$$