20ml of 0.4 M ${\mathrm{H}}_2{\mathrm{SO}}_4$and 80 ml of 0.2 M NaOH are mixed. Then, the pH of the resulting solution is

${\mathrm{H}}_2{\mathrm{SO}}_4 \mathrm{NaoH}$

${\mathrm{N}}_{\mathrm{a}}=0.4\times 2 {\mathrm{N}}_{\mathrm{b}}=0.2$

${\mathrm{V}}_{\mathrm{a}}=20 \mathrm{ml} {\mathrm{V}}_{\mathrm{b}}=80\mathrm{ml}$

${\mathrm{N}}_{\mathrm{a}}{\mathrm{V}}_{\mathrm{a}}= {\mathrm{N}}_{\mathrm{a}}{\mathrm{Y}}_{\mathrm{b}}=$

$0.8\times 20=16 80\times 0.2=16$

${\mathrm{N}}_{\mathrm{a}}{\mathrm{V}}_{\mathrm{a}}={\mathrm{N}}_{\mathrm{a}}{\mathrm{Y}}_{\mathrm{b}}$

∴   solution is neutral    

$\therefore \mathrm{PH}=7$