Alkaline earth metal nitrates are thermally unstable and disintegrate on heating.
All alkaline earth metals Nitrates decompose to form metal oxide, NO2 and O2.
Alkali metals carbonates are thermally stable and do not disintegrate even at high temperature.
Alkaline earth metals nitrates are soluble in water.
Their solubility reduces on moving down the group because their hydration energies decrease more rapidly than the lattice energies.
Alkali metals carbonates are soluble in water.
Their solubility increases on moving down the group, since the lattice energies decrease more rapidly than their hydration energies.
Final Answer:
Hence, alkaline earth metal nitrates are thermally unstable and water-soluble that decreases down the group. Alkali metals carbonates are thermally stable and have high solubility due to higher hydration energy.