The thermal stability order of the carbonates is

Options

A. `Na_(2)CO_(3)gt K_(2)CO_(3)gtBeCO_(3)gt BaCO_(3)`
B. `K_(2)CO_(3)gt Na_(2)CO_(3) gt BaCO_(3) gt BeCO_(3)`
C. `BaCO_(3)gtBeCO_(3)gtK_(2)CO_(3)gtNa_(2)CO_(3)`
D. `BeCO_(3)gt Na_(2)CO_(3)gt BaCO_(3) gt K_(2)CO_(3)`

Answer

To determine the thermal stability order of the carbonates, we will analyze the given carbonates: Na2CO3, K2CO3, BeCO3, and BaCO3. The thermal stability of carbonates generally depends on the cation size and its polarizing power. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Carbonates
We have the following carbonates to analyze:
- Sodium Carbonate (Na2CO3)
- Potassium Carbonate (K2CO3)
- Beryllium Carbonate (BeCO3)
- Barium Carbonate (BaCO3)

### Step 2: Understand Thermal Stability
The thermal stability of carbonates is influenced by the ionic or covalent character of the compounds. Generally, the more ionic a compound is, the higher its thermal stability. This is because ionic compounds require more energy to break the ionic bonds.

### Step 3: Analyze Cation Size and Charge
The cations in the carbonates are:
- Na+ (small size)
- K+ (larger size)
- Be2+ (small size, high charge)
- Ba2+ (larger size, lower charge density)

### Step 4: Apply Fajans' Rule
According to Fajans' rule, smaller cations with higher charge density will have a greater polarizing power, leading to more covalent character in the compound. Conversely, larger cations will have lower polarizing power and thus more ionic character.

### Step 5: Compare the Cations
- **Beryllium (Be2+)**: Small size, high charge → more covalent character.
- **Sodium (Na+)**: Small size, low charge → more ionic character than BeCO3.
- **Barium (Ba2+)**: Larger size, lower charge density → more ionic character than BeCO3.
- **Potassium (K+)**: Largest size among the alkali metals → least ionic character.

### Step 6: Determine the Order of Stability
Based on the analysis:
- K2CO3 has the highest ionic character and thus the highest thermal stability.
- Na2CO3 is next, as it is also ionic but has a smaller cation than K+.
- BaCO3 follows, as it has a larger cation than Na+.
- BeCO3 has the least stability due to its covalent character.

### Conclusion: Thermal Stability Order
The thermal stability order of the carbonates is:
**K2CO3 > Na2CO3 > BaCO3 > BeCO3**