Give the decreasing order of thermal stability of the following .

Options

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

Answer

To determine the decreasing order of thermal stability of the carbonates BeCO3, MgCO3, CaCO3, and BaCO3, we can follow these steps:

### Step 1: Identify the Cations
The carbonates in question are:
- BeCO3 (Beryllium Carbonate)
- MgCO3 (Magnesium Carbonate)
- CaCO3 (Calcium Carbonate)
- BaCO3 (Barium Carbonate)

The cations present are Beryllium (Be), Magnesium (Mg), Calcium (Ca), and Barium (Ba), which are all Group 2 elements (alkaline earth metals).

### Step 2: Understand the Trend in Group 2 Elements
As we move down the Group 2 elements from Be to Ba:
- The size of the cations increases due to the addition of electron shells.
- The nuclear charge increases, but the effect of increased shielding from inner electrons means that the effective nuclear charge experienced by the outer electrons does not increase proportionately.

### Step 3: Analyze Polarization
- Larger cations (like Ba) can polarize the carbonate ion (CO3^2-) more effectively than smaller cations (like Be).
- Increased polarization weakens the bond between carbon and oxygen in the carbonate ion, making it easier to break during thermal decomposition.

### Step 4: Determine Thermal Stability
- The thermal stability of carbonates decreases as the ability of the cation to polarize the carbonate ion increases.
- Therefore, the order of thermal stability from least stable to most stable is:
- BeCO3 < MgCO3 < CaCO3 < BaCO3

### Step 5: Write the Final Order
Thus, the decreasing order of thermal stability is:
**BaCO3 > CaCO3 > MgCO3 > BeCO3**