$K_{a_1}, K_{a_2}$ and $K_{a_3}$ are the respective ionisation constants for the following reactions.

$$\begin{aligned} & \mathrm{H}_2 \mathrm{~S} \rightleftharpoons \mathrm{H}^{+}+\mathrm{HS}^{-} \\ & \mathrm{HS}^{-} \rightleftharpoons \mathrm{H}^{+}+\mathrm{S}^{2-} \\ & \mathrm{H}_2 \mathrm{~S} \rightleftharpoons 2 \mathrm{H}^{+}+\mathrm{S}^{2-} \end{aligned}$$

The correct relationship between $K_{a_1}, K_{a_2}, K_{a_3}$ is

Acidity of $\mathrm{BF}_3$ can be explained on the basis of which of the following concepts?

Which of the following will produce a buffer solution when mixed i equal volumes?

In which of the following solvents is silver chloride most soluble?

What will be the value of pH of $0.01 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{CH}_3 \mathrm{COOH}$ $\left(K_a=1.74 \times 10^{-5}\right) ?$