Which among the following is correct conjugate acid base pair for the equation stated below?

$$\mathrm{HCl}+\mathrm{NH}_3 \rightleftharpoons \mathrm{NH}_4^{+}+\mathrm{Cl}^{-}$$

Dissociation constant and degree of dissociation of weak acid are $1.8 \times 10^{-5}$ and 0.03 respectively. What will be the concentration of solution of weak acid?

Which from following salts is NOT derived from weak acid and weak base?

Calculate the solubility product of sparingly soluble salt BA at $25^{\circ} \mathrm{C}$ if its solubility is $7.2 \times 10^{-7} \mathrm{~mol} \mathrm{~dm}^{-3}$ at same temperature.