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The correct order of increasing thermal stability of K2CO3, MgCO3, CaCO3 and BeCO3 is

1. BeCO3 < MgCO3 < CaCO3 < K2CO3
2. MgCO3 < BeCO3 < CaCO3 < K2CO3
3. K2CO3 < MgCO3 < CaCO3 < BeCO3
4. BeCO3 < MgCO3 < K2CO3 < CaCO3

Correct answer: BeCO3 < MgCO3 < CaCO3 < K2CO3

Solution

Thermal stability of carbonates increases down the group in the periodic table due to the increasing size of the cation, which reduces the polarizing power and stabilizes the carbonate ion. Potassium carbonate (K2CO3) is the most stable, while beryllium carbonate (BeCO3) is the least stable.

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