50 mL of 0.2 M ammonia solution is treated with 25 mL of 0.2 M HCl. If p K_b of ammonia solution is 4.75, the pH of the mixture will be:

$\displaystyle 50$ mL of $\displaystyle 0.2$ M ammonia solution is treated with $\displaystyle 25$ mL of $\displaystyle 0.2$ M HCl . If $\displaystyle \mathrm{p} K_{\mathrm{b}}$ of ammonia solution is $\displaystyle 4.75$, the pH of the mixture will be :