b
\(\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{(\mathrm{aq})}^{+}+\mathrm{OH}_{(\mathrm{aq})}^{-}\)

For ionization of \(\mathrm{H}_{2} \mathrm{O}: \Delta \mathrm{H}>\mathrm{O}\) \(\Rightarrow\) Endothermic

On temperature increase reaction shifts forward

\(\Rightarrow\) both \(\left[\mathrm{H}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\) increase

\(\Rightarrow \mathrm{pH} \;and\; \mathrm{pOH}\) decreases.