Which of the following alkaline earth metals has the greatest tendency to form covalent compounds?

Gypsum $CaSO_4 \cdot 2H_2O$ on heating to about $120 \, ^oC$ forms a compound which has the chemical composition represented by

Among the sulphates of alkaline earth metals,the solubilities of $BeSO_4$ and $MgSO_4$ in water,respectively,are

Which of the following elements shows a high tendency to form peroxide?

$A$ 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 $X$?
$\mathop X\limits_{solid}$ $\xrightarrow{\text{heating}} CO_2 + \text{residue}$ $\xrightarrow{H_2O} Y$ $\xrightarrow{\text{excess } CO_2} \mathop Z\limits_{\text{solution}}$ $\xrightarrow{\text{heating}} X$

Which of the following compounds does not show amphoteric behaviour?