Which process is associated with the production of sodium carbonate?

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?

Which of the following compounds liberates oxygen on heating?

The metal that produces $H_{2}$ with both dil. $HCl$ and $NaOH_{(aq)}$ is

Caesium is used in

The total number of elements among $S$,$P$,$Zn$,$Al$,$Sn$,$Pb$ which produce $H_2$ gas with $NaOH$ is