Which of the following order is correct for thermal stability?

Options

A. `MgCO_(3)lt CaCO_(3)ltBeCO_(3)`
B. `BeCO_(3)lt MgCO_(3)ltCaCO_(3)`
C. `CACO_(3)lt BeCO_(3)lt MgCO_(3)`
D. `CACO_(3)lt MgCO_(3)lt BeCO_(3)`

Answer

To determine the correct order of thermal stability for the given carbonates (Beryllium Carbonate, Magnesium Carbonate, and Calcium Carbonate), we need to analyze the factors affecting their stability.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have three carbonates to consider:
- Beryllium Carbonate (BeCO₃)
- Magnesium Carbonate (MgCO₃)
- Calcium Carbonate (CaCO₃)

2. **Understand Thermal Stability**: Thermal stability refers to the ability of a compound to resist decomposition upon heating. The more stable a compound is, the more energy (heat) is required to break it down into its constituent elements.

3. **Ionic vs. Covalent Character**: The stability of these carbonates can be influenced by the ionic or covalent character of the bonds. Generally, ionic compounds are more stable than covalent compounds because they have higher melting and boiling points.

4. **Cation Size and Charge Density**: As we move down the group in the periodic table, the size of the cation increases:
- Beryllium (Be²⁺) is smaller than Magnesium (Mg²⁺), which is smaller than Calcium (Ca²⁺).
- Smaller cations have higher charge density, which leads to greater polarizing power and thus a greater tendency to form covalent character with the anion (CO₃²⁻).

5. **Determine the Order of Stability**:
- **Beryllium Carbonate**: Has the highest covalent character due to the small size of Be²⁺, making it less thermally stable.
- **Magnesium Carbonate**: Intermediate stability, as Mg²⁺ is larger than Be²⁺ but smaller than Ca²⁺.
- **Calcium Carbonate**: Has the least covalent character and the highest ionic character, making it the most thermally stable.

6. **Conclusion**: Based on the analysis, the order of thermal stability from most stable to least stable is:
- Calcium Carbonate (CaCO₃) > Magnesium Carbonate (MgCO₃) > Beryllium Carbonate (BeCO₃).

### Final Answer:
The correct order for thermal stability is:
**CaCO₃ > MgCO₃ > BeCO₃**.