Which pair of atomic numbers represents $s$-block elements?

$A$ metal $M$ reacts with $N_2$ to give a compound '$A$' $(M_3N)$. '$A$' on heating at high temperature gives back '$M$' and '$A$' on reacting with $H_2O$ gives a gas '$B$'. '$B$' turns $CuSO_4$ solution blue on passing through it. $A$ and $B$ can be

The increasing order of solubility in water is:

Assertion $(A)$: Alkali metals are soft and have low melting and boiling points.
Reason $(R)$: This is because interatomic bonds are weak.

The decomposition of sodium nitrate at temperatures above $800 \, ^oC$ yields ...............

Which chloride does not exist as hydrate?