Give short explanations on salts of oxo-acids of alkali metal elements.

(N/A) Oxo-acids are compounds in which the acidic proton is on a hydroxyl group with an oxo group attached to the same atom.
Examples include carbonic acid,$H_{2}CO_{3}$ $(OC(OH)_{2})$,and sulphuric acid,$H_{2}SO_{4}$ $(O_{2}S(OH)_{2})$.
Alkali metals form salts with all oxo-acids. These salts are generally soluble in water and thermally stable.
Their carbonates $(M_{2}CO_{3})$ and,in most cases,their hydrogen carbonates $(MHCO_{3})$ are highly stable to heat.
As the electropositive character increases down the group,the stability of the carbonates and hydrogen carbonates increases.
Lithium carbonate is not thermally stable because the small $Li^{+}$ ion polarizes the large $CO_{3}^{2-}$ ion,leading to the formation of $Li_{2}O$ and $CO_{2}$. Additionally,lithium hydrogen carbonate does not exist as a solid.