$\mathrm{pOH}$ of ${\mathrm{H}}_2\mathrm{O}$ is 7.0 at 298 K. If water is heated at 350 K, which of the following statement should be true? 

$\mathrm{pOH}$ of ${\mathrm{H}}_2\mathrm{O}$ $=7.0\text{ (at }298\mathrm{K}\text{ ) }$

Le Chattier's principles state that forward reaction is preferred because it absorbs heat. As a result, when the temperature rises, the excess heat would be absorbed.

${\mathrm{H}}_2\mathrm{O}+{\mathrm{H}}_2\mathrm{O}\leftrightharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{OH}}^{-}$

⟶ the pH falls, as temperature increases.

⟶ also the pOH decreases since the value of ${\mathrm{pK}}_{\mathrm{w}}$ itself decreases.