Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals.
$(a)$ Nitrates $(b)$ Carbonates $(c)$ Sulphates.

(N/A) Nitrates :
$(i)$ Thermal stability: Nitrates of alkali metals,except $LiNO_{3}$,decompose on strong heating to form nitrites. $2KNO_{3(s)} \rightarrow 2KNO_{2(s)} + O_{2(g)}$. $LiNO_{3}$ on decomposition gives oxide: $4LiNO_{3(s)} \xrightarrow{\Delta} 2Li_{2}O_{(s)} + 4NO_{2(g)} + O_{2(g)}$. As we move down group-$1$ and group-$2$,the thermal stability of nitrates increases.
$(ii)$ Solubility: Nitrates of both group-$1$ and group-$2$ metals are soluble in water.
$(b)$ Carbonates :
$(i)$ Thermal stability: The carbonates of alkali metals are stable towards heat,except $Li_{2}CO_{3}$,which decomposes to form lithium oxide. The carbonates of alkaline earth metals decompose on heating to form oxide and carbon dioxide. $Na_{2}CO_{3} \xrightarrow{\Delta} \text{No reaction}$. $Li_{2}CO_{3} \xrightarrow{\Delta} Li_{2}O + CO_{2}$. $MgCO_{3} \xrightarrow{\Delta} MgO + CO_{2}$.
$(ii)$ Solubility: Carbonates of alkali metals are soluble in water with the exception of $Li_{2}CO_{3}$. Solubility increases down the group. Carbonates of alkaline earth metals are generally insoluble in water.
$(c)$ Sulphates :
$(i)$ Thermal stability: Sulphates of both group-$1$ and group-$2$ metals are stable towards heat.
$(ii)$ Solubility: Sulphates of alkali metals are soluble in water. Sulphates of alkaline earth metals show varied trends: $BeSO_{4}$ (fairly soluble),$MgSO_{4}$ (soluble),$CaSO_{4}$ (sparingly soluble),$SrSO_{4}$ (insoluble),$BaSO_{4}$ (insoluble). Solubility of alkaline earth metal sulphates decreases down the group.