Concentration of the ${\mathrm{Ag}}^{+}$ ions in a saturated solution of ${\mathrm{Ag}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ is $2.24\times {10}^{-4} \mathrm{mol} {\mathrm{L}}^{-1}$  solubility product of ${\mathrm{Ag}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ is

Following solutions were prepared by mixing different volumes of $\mathrm{NaOH}$ of $\mathrm{HCl}$ different concentrations

(i) $60 \mathrm{mL} \frac{\mathrm{M}}{10} \mathrm{HCl} + 40\mathrm{mL} \frac{\mathrm{M}}{10} \mathrm{NaOH}$                 (ii) $55\mathrm{mL} \frac{\mathrm{M}}{10} \mathrm{HCl} + 45\mathrm{mL} \frac{\mathrm{M}}{10} \mathrm{NaOH}$

(iii) $75 \mathrm{mL} \frac{\mathrm{M}}{5} \mathrm{HCl} + 25\mathrm{mL} \frac{\mathrm{M}}{5} \mathrm{NaOH}$               (iv) $100 \mathrm{mL} \frac{\mathrm{M}}{10} \mathrm{HCl} + 100\mathrm{mL} \frac{\mathrm{M}}{10} \mathrm{NaOH}$

$\mathrm{pH}$ of which one of them is equal to $1$?