What is the value of $K_{s p}$ for saturated solution of $\mathrm{Ba}(\mathrm{OH})_2$ having pH 12 ?

What is the pH of buffer solution prepared by mixing 0.01 M weak acid and 0.02 M salt of weak acid with strong base? $\left(\mathrm{pK}_{\mathrm{a}}=4.680\right)$

If pH of solution changes from 4 to 5 , then the $\mathrm{H}_3 \mathrm{O}^{+}$ion concentration of solution

Which from following substances acts as a base when reacted with water?