Explanation: Solve: \( \text{NH}_3 + \text{H}^+ \rightarrow \text{NH}_4^+ \) ক্ষারক অনুবর্তী অম্ল \[ K_{a,\text{NH}_3} \times K_{a,\text{NH}_4^+} = 10^{-14} \] \[ \implies K_{a,\text{NH}_4^+} = \frac{10^{-14}}{K_{a,\text{NH}_3}} = \frac{10^{-14}}{1.8 \times 10^{-5}} = 5.56 \times 10^{-10} \]