Discuss the trend of the following:
$(i)$ Thermal stability of carbonates of Group $-2$ elements.
$(ii)$ The solubility and the nature of oxides of Group $-2$ elements.

(N/A) $(i)$ Thermal stability increases down the group. On heating,these carbonates decompose to give $CO_{2}$ and the corresponding oxide of the Group $-2$ element.
$BeCO_{3} < MgCO_{3} < CaCO_{3} < SrCO_{3} < Ba_{CO_{3}}$
$BeCO_{3}$ is unstable and is kept stable in an atmosphere of $CO_{2}$.
$BeCO_{3} \rightleftharpoons BeO + CO_{2}$
$(ii)$ All oxides are basic and ionic in nature except $BeO$,which is amphoteric and covalent. Lattice energy of oxides decreases as the size of the cation increases. Basic nature increases down the group.
Except $BeO$ and $MgO$,all oxides are soluble in water and produce a large amount of heat upon dissolution. $BeO$ and $MgO$,due to their high lattice energy,are insoluble in water.