Very pure hydrogen (99.9%) can be made by which of the following processes ?

Hydrogen of high purity is obtained by electrolyzing aqueous barium hydroxide in presence of Ni electrodes.

$$\begin{gathered} 2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{e}}^{-} \stackrel{ }{\to } 2{\mathrm{OH}}^{-} + {\mathrm{H}}_2 \\ 2{\mathrm{OH}}^{-} \stackrel{ }{\to }{\mathrm{H}}_2\mathrm{O} + \frac{1}{2} {\mathrm{O}}_2 + 2{\mathrm{e}}^{-} \end{gathered}$$