If one mole of $\mathrm{Ba}{\left(\mathrm{OH}\right)}_2$ is added to 10 litres of water at 25 °C, the pH of the resultant solution would be

Barium hydroxide is a chemical compound with the chemical formula Ba(OH)₂. The monohydrate, known as baryta or baryta-water, is one of the principal compounds of barium. This white granular monohydrate is the usual commercial form.

$\mathrm{Ba}{\left(\mathrm{OH}\right)}_2$ completely ionizes in water.

Hence, $\left[{\mathrm{OH}}^{-}\right]=0.2\mathrm{M},\mathrm{pOH}=-\log \left(0.2\right)=0.7,\mathrm{pH}=14-0.7=13.3$