$Mg(NO_3)_2 \cdot XH_2O$ and $Ba(NO_3)_2 \cdot YH_2O$ represent the formulas of the crystalline forms of nitrate salts. The sum of $X$ and $Y$ is $.........$.

The element having atomic number $56$ belongs to

The product obtained on fusion of $BaSO_4$ and $Na_2CO_3$ is

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

Plaster of Paris is used:

Identify the correct statements from the following:
$I$. All alkaline earth metals give hydrides on heating with hydrogen.
$II$. Calcium hydroxide is used to purify sugar.
$III$. $BeCl_2$ is a dimer in gaseous phase.