When gypsum is heated to $393 \; K$,it forms

The ionic carbide is

The increasing order of reactivity of alkaline earth metals with water is

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Beryllium has a less negative value of reduction potential compared to the other alkaline earth metals.
Reason $R:$ Beryllium has large hydration energy due to the small size of $Be^{2+}$ but a relatively large value of atomization enthalpy.
In the light of the above statements,choose the most appropriate answer from the options given below.

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

Plaster of Paris is used: