20 mL of 0.1 M H_2 SO_4 solution is added to 30 mL of 0.2 M NH_4 OH solution. The pH of the resultant mixture is: [ pk_b. of NH_4 OH =4.7 ].

$\displaystyle 20$ mL of $\displaystyle 0.1 \mathrm{M} \mathrm{H}_2 \mathrm{SO}_4$ solution is added to $\displaystyle 30$ mL of $\displaystyle 0.2 \mathrm{M} \mathrm{NH}_4 \mathrm{OH}$ solution. The pH of the resultant mixture is : $\displaystyle \left[\mathrm{pk}_{\mathrm{b}}\right.$ of $\displaystyle \mathrm{NH}_4 \mathrm{OH}=4.7$ ].