Which of the following does not contain $Mg$:

Lithium shows diagonal relationship with element $X$ and aluminum with $Y$. $X$ and $Y$ respectively are

The white precipitate $(Y)$, obtained on passing a colourless and odourless gas $(X)$ through an ammoniacal solution of $NaCl$, loses about $37 \%$ of its weight on heating and a white residue $(Z)$ of basic nature is left. Identify $(X)$, $(Y)$, and $(Z)$ from the following sets.

When $CO_2$ gas is passed through an aqueous solution of $Na_2CO_3$,what is formed?

Why are alkali metals not found in nature?

Which alkali metal emits blue colour light in a flame test?