The solubilities of carbonates decrease down the magnesium group due to a decrease in
- hydration energies of cations
- lattice energies of solids
- inter-ionic attraction
- entropy of solution formation
The stability of the carbonates of the alkaline earth metals increases on moving down the group. The solubility of carbonate of metals in water is generally low. However, they dissolve in water containing CO2 yielding bicarbonates, and this solubility decreases on going down in a group with the increase in stability of carbonates of metals, and decrease in hydration energy of the cations.
The correct option is A.