Which one of the alkaline earth metal carbonates is thermally the most stable?
1. `MgCO_3` 2. CaCO_3` 3. SrCO_3` 4. BaCO_3`

Explanation

`BaCO_3` , Explanation: Among all the alkaline earth metals, `Ba^(2+)` ion is the largest. Again, `CO_3^(2-)` ion is also quite large in size. Thus, among the given carbonates, `Ba^(2+) and CO_3^(2-)` ions are most tightly packed in the crystal lattice of `BaCO_3`. Consquently, lattice enthalpy of `BaCO_3` is the highest and so, it is most thermally stable.