Unknown inorganic compound ' $A$ ' is used for water softening. ' $A$ ' reacts with $\mathrm{Na}_2 \mathrm{CO}_3$ to generate an alkaline compound ' $B$ ' whose $\mathrm{pH}=14$. ' $A$ ' on reaction with $\mathrm{CO}_2$ gives cloudy ppt. ' $B$ ' +CaO reacts with unknown organic compound ' $C$ ' to give $\mathrm{C}_6 \mathrm{H}_6$. $A$, $B$ and $C$, respectively, are

The correct order of melting points of the following salts is

$$ \begin{array}{lll} \text { LiCl } & \text { LiF } & \text { Lil } \\ \text { I } & \text { II } & \text { III } \end{array} $$

Which of the following salts can accommodate more number of $\mathrm{H}_2 \mathrm{O}$ molecules per molecule in their halide hydrates?

Potassium superoxide on hydrolysis gives