The molar solubility of $\mathrm{PbI}_2$ in $0.2 \mathrm{MPb}\left(\mathrm{NO}_3\right)_2$ solution in terms of $K_{s p}$ (solubility product) is

The percentage of ionisation of 1 L of $x \mathrm{M}$ acetic acid is 4.242 and is called solution " $A$ ". The percentage of ionisation of 1 L of $y \mathrm{M}$ acetic acid is 3 and is called solution " $B$ ". Solution " $A$ " is mixed with solution " $B$ ". What is the concentration of acetic acid in the resultant solution? ( $K_{\mathrm{a}}$ of acetic acid $=1.8 \times 10^{-5}$ )

At $25^{\circ} \mathrm{C}, K_a$ of formic acid is $1.8 \times 10^{-4}$. What is the $K_b$ of $\mathrm{HCOO}^{-}$?