$\begin{aligned} & \mathrm{HF}:\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=M \cdot \alpha=2 \times 2 / 4 \times 10^{-2}=48 \times 10^{-3} \\ & {\left[\mathrm{OH}^{-}\right] \times\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=10^{-14} \Rightarrow\left[\mathrm{OH}^{-}\right]=\frac{10^{-14}}{48 \times 10^{-3}}=\frac{1}{48} \times 10^{-11}} \\ & \mathrm{NH}_3:\left[\mathrm{OH}^{-}\right]=M \cdot \alpha \cdot n=3 \times 0 / 8 \times 1=24 \times 10^{-1} \\ & {\left[\mathrm{OH}^{-}\right] \times\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=10^{-14} \Rightarrow\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=\frac{10^{-14}}{24 \times 10^{-1}}=\frac{1}{24} \times 10^{-13}} \\ & \Rightarrow \frac{\left[\mathrm{OH}^{-}\right]_{\mathrm{HF}}}{\left[\mathrm{H}_3 \mathrm{O}^{+}\right]_{\mathrm{NH}_3}}=\frac{\frac{1}{48} \times 10^{-11}}{\frac{1}{24} \times 10^{-13}}=\frac{100}{2}=50\end{aligned}$