What are the products formed when $Li_2CO_3$ undergoes thermal decomposition?

Statement $A$: Extraction of magnesium is done by the electrolysis of a molten mixture of $MgCl_2$,$NaCl$,and $CaCl_2$.
Reason $R$: Calcium chloride acts as a reducing agent.

$Sodium$ metal is highly reactive and cannot be stored under:

The word 'alkali' used for alkali metals indicates:

Which of the following has the highest value of cohesive energy?

Comment on each of the following observations:
$(a)$ The mobilities of the alkali metal ions in aqueous solution are $Li^{+} < Na^{+} < K^{+} < Rb^{+} < Cs^{+}$
$(b)$ Lithium is the only alkali metal to form a nitride directly.
$(c)$ The standard electrode potential $E^{\circ}$ for the reaction $M^{2+}_{(aq)} + 2e^{-} \to M_{(s)}$ (where $M = Ca, Sr$ or $Ba$) is nearly constant.