Which among the following elements of group-$2$ exhibits anomalous properties?

$A$ white solid '$A$' on heating gives off a gas which turns lime water milky. The residue is yellow when hot but turns white on cooling. This solid '$A$' is

In the hardening stage of Plaster of Paris, the compound formed is:

Which one of the following is fluorspar?

Assertion : Of the various chlorides of alkaline earth metals $BeCl_2$ is covalent in nature,whereas $MgCl_2$ and $CaCl_2$ are ionic compounds.
Reason : $Be$ is the first member of group $2$.

Which one of the following alkaline earth metals does not form hydride when it is heated with hydrogen directly?