Bleaching powder is a compound having the molecular formula

$A$ pink colored salt on dry heating becomes blue in colour. The salt may contain:

$A$ red coloured mixed oxide $(X)$ on treatment with conc. $HNO_3$ gives a compound $(Y).$ $(Y)$ with $HCl$ produces a chloride compound $(Z)$ which can also be produced by treating $(X)$ with conc. $HCl.$ Compounds $(X),$ $(Y),$ and $(Z)$ will be

For a good quality cement,the ratio of lime to the total of the oxides of $Si$,$Al$ and $Fe$ should be as close as to :

$A$ white solid '$A$' on heating produces a gas that turns lime water milky,and the remaining solid residue is yellow when hot but turns white on cooling. The solid '$A$' is:

Arrange the following in the correct order of thermal stability:
$K_2CO_3, MgCO_3, CaCO_3, BeCO_3$