Which of the following alkaline earth metals does not exhibit colour when heated in a flame?

$A$ substance absorbs $CO_2$ and violently reacts with water. That substance is

The outer electronic configuration of alkaline earth metals is:

Assertion $(A)$: $Be$ and $Mg$ do not impart any colour to the flame.
Reason $(R)$: The electrons in them are too strongly bound to get excited by the energy of the flame.
The correct option among the following is:

Which element among the alkaline earth metals primarily forms covalent compounds?

Heating a solid compound $X$ produces $CO_2$ gas and a residue. Adding water to this residue produces compound $Y$. Passing excess $CO_2$ gas through a solution of $Y$ produces a clear solution $Z$. Boiling $Z$ regenerates compound $X$. What is compound $X$?