Water is periodically sprinkled on cement plasters during curing. What does this help in?

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$a$. $Ca(OCl)_2$	$i$. Antacid
$b$. $CaSO_4 \cdot \frac{1}{2} H_2O$	$ii$. Cement
$c$. $CaO$	$iii$. Bleach
$d$. $CaCO_3$	$iv$. Plaster of Paris

Choose the most appropriate answer from the options given below:

Lime reacts exothermally with water to give '$A$' which has low solubility in water. Aqueous solution of '$A$' is often used for the test of $CO_{2}$,a test in which insoluble $B$ is formed. If $B$ is further reacted with $CO_{2}$ then a soluble compound is formed. '$A$' is

$X + C + Cl_2 \xrightarrow{1000 \ K} Y + CO;$
$Y + 2H_2O \rightarrow Z + 2HCl$
Compound $Y$ is found in a polymeric chain structure and is an electron-deficient molecule. $Y$ must be:

Beryllium and magnesium do not give colour to flame whereas other alkaline earth metals do so. Why?

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