What is the use of the alloy of lithium and lead (white metal)?

$Na_2CO_3$ is manufactured by the Solvay process. The products that are recycled are:

State as to why:
$(a)$ a solution of $Na_2CO_3$ is alkaline?
$(b)$ alkali metals are prepared by electrolysis of their fused chlorides?
$(c)$ sodium is found to be more useful than potassium?

The alkali metal with the lowest $E^{\circ}_{M^{+}/M} (V)$ is $X$ and the alkali metal with the highest $E^{\circ}_{M^{+}/M} (V)$ is $Y$. Then $X$ and $Y$ are respectively:

Nitrates of all the metals are

Write balanced chemical equations for the reactions between:
$(a)$ $Na_{2}O_{2}$ and water
$(b)$ $KO_{2}$ and water
$(c)$ $Na_{2}O$ and $CO_{2}$