The ${\mathrm{P}}^{\mathrm{H}}$ of a solution obtained by mixing $50\mathrm{mL}$ of $1\mathrm{M} \mathrm{HCl}$ and $30\mathrm{mL}$ of $1\mathrm{M} \mathrm{NaOH}$ is $\mathrm{x}\times {10}^{-4}$. the value of x is ______(nearest integer) $(\log 2.5=0.3979)$
 

$$\begin{gathered} \mathrm{HCl}(\mathrm{aq}.)+\mathrm{NaOH}(\mathrm{aq}.)\to \mathrm{NaCl}(\mathrm{aq}.)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{initial} 50 \mathrm{mmol} 30 \mathrm{mmol} - - \\ \text{⨍ inal 20 mmol 20 20 } \\ \left[\mathrm{HCl}\right]=\frac{20}{80}=\frac{1}{4}\mathrm{M}=2.5\times {10}^{-1}\mathrm{M} \\ {\mathrm{P}}^{\mathrm{H}}=-\log 2.5\times {10}^{-1}=1-0.3979=0.6021 \\ {\mathrm{P}}^{\mathrm{H}}=6021\times {10}^{-4} \end{gathered}$$