The most thermally unstable carbonate among thefollowing is

Options

A. `CaCO_3`
B. `MgCO_3`
C. `BeCO_3`
D. `BaCO_3`

Answer

To determine the most thermally unstable carbonate among the given options, we need to analyze the thermal stability of the carbonates of the alkaline earth metals (Group 2 elements). The carbonates in question are:

1. Beryllium carbonate (BeCO₃)
2. Magnesium carbonate (MgCO₃)
3. Calcium carbonate (CaCO₃)
4. Strontium carbonate (SrCO₃)

### Step-by-Step Solution:

1. **Identify the Group**: The carbonates mentioned belong to the alkaline earth metals, which are located in Group 2 of the periodic table.

2. **Understand Thermal Stability**: The thermal stability of carbonates generally increases as we move down the group in the periodic table. This is due to the increasing size of the metal cation, which leads to a weaker lattice energy and thus a more stable compound.

3. **Analyze Each Carbonate**:
- **Beryllium carbonate (BeCO₃)**: This is the smallest cation and is known to be the least thermally stable among the alkaline earth metal carbonates.
- **Magnesium carbonate (MgCO₃)**: More stable than beryllium carbonate but less stable than calcium and strontium carbonates.
- **Calcium carbonate (CaCO₃)**: More thermally stable than magnesium carbonate.
- **Strontium carbonate (SrCO₃)**: The most thermally stable carbonate among the options given.

4. **Conclusion**: Since beryllium carbonate is the least stable, it is the most thermally unstable carbonate among the options provided.

Thus, the answer is **Beryllium carbonate (BeCO₃)**.