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

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

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

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

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

The $\mathrm{pH}$ of which one of them will be equal to $1$?