An alkaline earth metal $M$ readily forms water-soluble sulphate and water-insoluble hydroxide. Its oxide $MO$ is very stable to heat and does not have rock-salt structure. $M$ is :-

Observe the following reactions:
$Dimer \longleftarrow \text{Vapour phase } MCl_2 \xrightarrow{1200 \ K} \text{linear monomer}$.
What is $M$?

The thermal stability of $BaCO_3$,$CaCO_3$,$SrCO_3$,and $MgCO_3$ decreases in the order:

The metal $X$ is prepared by the electrolysis of fused chloride. It reacts with hydrogen to form a colourless solid from which hydrogen gas is released on treatment with water. The metal is

Alkaline earth metals belong to the

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: