Which of the following components of cement is present in the highest amount?

The most electropositive amongst the alkaline earth metals 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:

Consider the following reaction sequence:
$CaO + CO_2 \to A$
$A \xrightarrow{\Delta} B + CO_2$
$B + H_2O \to C$
$C + CO_2 \to D$
$D + H_2O + CO_2 \to E$
Identify compounds $D$ and $E$.

Identify the correct statements with respect to compounds of Beryllium:
$I$. Beryllium oxide is amphoteric in nature.
$II$. Beryllium hydride is formed by the reaction of beryllium with hydrogen.
$III$. Beryllium hydride is formed by the reaction of beryllium chloride with lithium aluminium hydride.
$IV$. Beryllium sulphate is the least soluble sulphate among the sulphates of alkaline earth metals.

Among the alkaline earth metals,the element forming predominantly covalent compounds is: