What is the $pH$ of the solution formed by mixing $25.0 mL$ of a $0.15 M$ solution of $NH3$ with $25.0 mL$ of $0.12 M HCl$? $\left(K_b\text{ for }{\mathrm{NH}}_3=1.8\times {10}^{-5}\right)$

${\mathrm{NH}}_3 + {\mathrm{H}}^{+} ⟶{ \mathrm{NH}}_4^{+}$

25 X 0.15     25 X 0.12v

25 X 0.03          -                   25 X 0.12

$\mathrm{pOH}=p{K}_b+\log \frac{0.12}{0.03}$

$=4.74+0.6=5.34$

$\mathrm{pH}=8.66$

Hence, option C is correct.