Select the correct statement from the following.

Portland cement contains '$X$' to enhance the setting time. What is '$X$'?

$A$ metal is burnt in air and the ash on moistening smells of $NH_3$. The metal is

The setting of Plaster of Paris is associated with which of the following?

What are the products formed when an aqueous solution of magnesium bicarbonate is boiled?

$A$ solid compound $X$ on heating gives $CO_2$ gas and a residue. The residue mixed with water forms compound $Y$. On passing excess $CO_2$ gas through $Y$,a clear solution $Z$ is formed. On heating $Z$,compound $X$ is recovered. What is compound $X$?
$\mathop X\limits_{solid}$ $\xrightarrow{\text{heating}} CO_2 + \text{residue}$ $\xrightarrow{H_2O} Y$ $\xrightarrow{\text{excess } CO_2} \mathop Z\limits_{\text{solution}}$ $\xrightarrow{\text{heating}} X$