Which alkaline earth metal carbonate is the most thermally stable: ${\text{BeCO}}_3$, ${\text{MgCO}}_3$, ${\text{CaCO}}_3$, or ${\text{BaCO}}_3$?

Solution

1. Thermal decomposition of carbonates follows the reaction ${\text{MCO}}_3\to \text{MO}+{\text{CO}}_2$.
2. Stability increases as the ionic character of the metal-oxygen bond increases.
3. Down the group, the size of the cation increases, which decreases the polarizing power of the cation on the carbonate ion.
4. Barium has the largest ionic radius among the group 2 elements, making ${\text{BaCO}}_3$ the most stable.
5. Hence the answer is (D).