Metal carbonates decompose on heating to give metal oxide and carbon dioxide. Which of the metal carbonates is most stable thermally?

Options

A. `MgCO_(3)`
B. `CaCO_(3)`
C. `SrCO_(3)`
D. `BaCO_(3)`

Explanation

To determine which metal carbonate is the most thermally stable, we need to analyze the thermal decomposition of metal carbonates, specifically those of the alkaline earth metals. The general decomposition reaction for a metal carbonate (MCO3) is:

\[ \text{MCO}_3 \rightarrow \text{MO} + \text{CO}_2 \]

Where:
- MCO3 = Metal carbonate
- MO = Metal oxide
- CO2 = Carbon dioxide

### Step-by-Step Solution:

1. **Identify the Metal Carbonates**:
The alkaline earth metals include Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba). Therefore, the metal carbonates we are considering are:
- BeCO3
- MgCO3
- CaCO3
- SrCO3
- BaCO3

2. **Understand Thermal Stability**:
The thermal stability of a carbonate is influenced by the stability of the resulting metal oxide (MO) after decomposition. A more stable oxide will indicate a more stable carbonate.

3. **Analyze the Stability Trend**:
As we move down the group in the periodic table (from Be to Ba), the size of the metal cation increases. This affects the stability of the metal oxides:
- Smaller cations (like Be and Mg) form more stable oxides compared to larger cations (like Ba).
- The stability of the metal oxides decreases as the size of the cation increases because the small oxide ion (O^2-) is less stable with larger cations.

4. **Conclusion on Stability**:
- Barium (Ba) is the largest cation among the alkaline earth metals. Therefore, its oxide (BaO) is less stable compared to the oxides of the smaller cations.
- Consequently, the carbonate of barium (BaCO3) is the most thermally stable because it is less likely to decompose compared to the carbonates of the smaller alkaline earth metals.

5. **Final Answer**:
Thus, the most thermally stable metal carbonate is **Barium Carbonate (BaCO3)**.