Out of $BeF_{2}, MgF_{2}, CaF_{2}, SrF_{2}$,which has maximum solubility?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Barium carbonate is insoluble in water and is highly stable.
Reason $R$: The thermal stability of the carbonates increases with increasing cationic size.
Choose the most appropriate answer from the options given below for $A$ and $R$.

Give two uses of $calcium \ carbonate$ $(CaCO_3)$?

$A$ 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

$MgCl_2 \cdot 6H_2O$ when heated gives:

Which is not a similar characteristic about the electronic configuration of $Be, Mg, Ca$?