$A$ metal is burnt in air and the ash on moistening smells of $NH_3$. The metal is

$A$ solid compound $X$ on heating gives $CO_2$ gas and a residue. The residue mixed with water forms $Y$. On passing an excess of $CO_2$ through $Y$ in water,a clear solution $Z$ is obtained. On boiling $Z$,compound $X$ is reformed. The compound $X$ is

$A$ pair of substances which gives the same products on reaction with water is

What are $X$,$Y$ and $Z$ in the following reactions?
$CaCO_3 \stackrel{\Delta}{\rightleftharpoons} CO_2 + X$
$X + H_2O \longrightarrow Y$
$Y + Cl_2 \longrightarrow Z$

Which element among the alkaline earth metals primarily forms covalent compounds?

The property of the alkaline earth metals that increases with their atomic number is