Arrange the alkaline earth metal carbonate in the decreasing order of thermal stability .

Explanation

To arrange the alkaline earth metal carbonates in decreasing order of thermal stability, we need to consider the thermal stability trends of these carbonates as we move down the group in the periodic table. The alkaline earth metals include Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

### Step-by-Step Solution:

1. **Identify the Carbonates**: The alkaline earth metal carbonates we are considering are:
- Beryllium carbonate (BeCO3)
- Magnesium carbonate (MgCO3)
- Calcium carbonate (CaCO3)
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