pH Questions

Calculate the $\text{pOH}$ of a solution at $25{}^{\circ }\text{C}$ that contains $1\times 10^{-10}\text{ M}$ of hydronium ions.

Equimolar solutions of the following were prepared in water separately. Which one of the solutions will record the highest pH?

In a buffer solution containing equal concentration of ${\text{B}}^{-}$ and $\text{HB}$, the $K_b$ for ${\text{B}}^{-}$ is $10^{-10}$. The $\text{pH}$ of the buffer solution is:

If $\text{pH}$ of a saturated solution of ${\text{Ba(OH)}}_2$ is $12$, the value of its $K_{sp}$ is:

Equimolar solutions of the following substances were prepared separately. Which one of these will record the highest pH value?