Mortar is a mixture of which of the following?

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.

The thermal stability of alkaline earth metal carbonates $MgCO_{3}$,$CaCO_{3}$,$SrCO_{3}$,and $BaCO_{3}$ follows the order:

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

In the hardening stage of Plaster of Paris, the compound formed is:

Which group consists entirely of metals?