Calculate the pOH of 0 . 10 MHCl solution.

We know that $\mathrm{pOH}$ is a measure of hydroxide ion $\left({\mathrm{OH}}^{-}\right)$ concentration and the given concentration of ${\mathrm{H}}^{+}$ is $0.10 \mathrm{M}$

We are also familiar with the relation between $\mathrm{pH}$ and $\mathrm{pOH}$ i.e. 

$\mathrm{pH} + \mathrm{pOH} = 14$ 

$$\begin{gathered} \mathrm{pH}=-\log \left[{\mathrm{H}}^{+}\right]=-\log \left(0.1\right)=1 \\ \mathrm{pOH}=14-\mathrm{pH}=13 \end{gathered}$$