The value of ${\mathrm{P}}^{{\mathrm{K}}_{\mathrm{w}}}\text{ at }{90}^{\circ }\mathrm{C}$  is 12. Equal volumes of two solutions having  ${\mathrm{P}}^{\mathrm{H}}=2,{\mathrm{P}}^{\mathrm{H}}=10$ are mixed. Then the P^H of the resulting solution at ${90}^{\circ }\mathrm{C}$ is

${\mathrm{P}}^{\mathrm{H}}=6,$since the solution is neutral.

At 90⁰

${\mathrm{P}}^{\mathrm{H}} = 2, \left[{\mathrm{H}}^{+}\right]={10}^{-2}$

${\mathrm{P}}^{\mathrm{H}}=10;\left[{\mathrm{OH}}^{-}\right]={10}^{-2}$

Mixture is containing equal concentration of [H⁺] and [OH^-]. Solution is neutral.