100 ml of 0.1 M ${\mathrm{HNO}}_3$ and 400 ml of 0.1 M ${\mathrm{H}}_2{\mathrm{SO}}_4$are mixed. Proton concentration of the mixture is

$\left[{\mathrm{H}}^{+}\right]=$Normality of strong acid;

$$\begin{gathered} {\mathrm{V}}_{\mathrm{a}}{\mathrm{N}}_{\mathrm{a}}\left({\mathrm{HNO}}_3\right)=100\left(0.1\mathrm{M}\right)1=10 ; \\ {\mathrm{V}}_{\mathrm{a}}{\mathrm{N}}_{\mathrm{a}}\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)=400\left(0.1\mathrm{M}\right)2=80 ; \\ \left[{\mathrm{H}}^{+}\right]={\frac{{\mathrm{V}}_1{\mathrm{N}}_1+{\mathrm{V}}_2{\mathrm{N}}_2}{{\mathrm{V}}_1+{\mathrm{V}}_2}}_{ }; \\ \left[{\mathrm{H}}^{+}\right]=\frac{10+80}{500}=0.18\mathrm{M} \end{gathered}$$