What minimum $\mathrm{pH}$ must be maintained in a saturated ${\mathrm{H}}_2\mathrm{S}$ solution $(0.1 \mathrm{M})$ to avoid precipitation of both ${\mathrm{Mn}}^{2+} \text{and} {\mathrm{Fe}}^{2+}$ from a solution, in which each ion is present at a concentration of $0.01 \mathrm{M}?$

$\left({\mathrm{K}}_{\mathrm{a}}\right.$of ${\mathrm{H}}_2\mathrm{S}=9.6\times {10}^{-21}; {\mathrm{K}}_{\mathrm{sp}}$ of $\mathrm{MnS}=2.5\times {10}^{-13}; {\mathrm{K}}_{\mathrm{sp}}$ of$\left.\mathrm{FeS}=6.4\times {10}^{-18}\right)$

The solubility product of ${\mathrm{Ag}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ at $25° \mathrm{C}$ is $1.29\times {10}^{-11}{\mathrm{mol}}^3{\mathrm{L}}^{-3}.$ A solution of ${\mathrm{K}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ containing
$0.152$ mole in $500 \mathrm{mL}$ water.is shaken with an excess of ${\mathrm{Ag}}_2{\mathrm{CO}}_3$ till the following equilibrium is reached:

${\mathrm{Ag}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)+{\mathrm{K}}_2{\mathrm{C}}_2{\mathrm{O}}_4\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{Ag}}_2{\mathrm{C}}_2{\mathrm{O}}_4\left(\mathrm{s}\right)+{\mathrm{K}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)$.

At equilibrium, the solution contains $0.0358$ mole of ${\mathrm{K}}_2{\mathrm{CO}}_3$. Assuming the degree of dissociation of ${\mathrm{K}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ and ${\mathrm{K}}_2{\mathrm{CO}}_3$ to be equal, if the solubility product of ${\mathrm{Ag}}_2{\mathrm{CO}}_3$ is $3.794\times {10}^{-\mathrm{x}} {\mathrm{mol}}^3{\mathrm{L}}^{-3}$, find $\mathrm{x}.$

$\mathrm{C} \mathrm{M}$ fluoroacetic acid solution was found to contain $\left[{\mathrm{H}}^{+}\right]=1.5\times {10}^{-3} \mathrm{M}. {\mathrm{K}}_{\mathrm{a}}$ of fluoroacetic acid $=2.5\times {10}^{-3}$. Then:

Which of the following statement/s is/are correct about weak acids in aqueous solutions?

I. When $\mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}$ of a monoprotic acid, $50\%$ of the acid is ionised
Il. If $\mathrm{pH}={\mathrm{pKa}}_2$ of a diprotic acid, the average charge of all the ionised species is $0.5$
Ill. When $\mathrm{pH}=\mathrm{pKa}+1, 10\%$ of the acid is ionised
IV. When $\mathrm{pH}=7, 50\%$ of a monibasic acid is ionized.