20 mL of $0.1 \mathrm{M} \mathrm{NH}_4 \mathrm{OH}$ is mixed with 40 mL of 0.05 M HCl . The pH of the mixture is nearest to:
(Given: $\mathrm{K}_{\mathrm{b}}\left(\mathrm{NH}_4 \mathrm{OH}\right)=1 \times 10^{-5}, \log 2=0.30$,
$$
\log 3=0.48, \log 5=0.69, \log 7=0.84, \log 11=1.04)
$$
