Which of the following thermal stability order is not correct :-

Options

A. `NaHCO_(3) lt KHCO_(3) lt RbHCO_(3)`
B. `CaO_(2) gt SrO_(2) gt BaO_(2)`
C. `Na_(2)SO_(4) gt MgSO_(4) gt Al_(2)(SO_(4))_(3)`
D. `C Cl_(4) gt SiCl_(4) gt GeCl_(4) gt SnCl_(4)`

Explanation

To determine which order of thermal stability is incorrect, we need to analyze the thermal stability of different compounds based on their group in the periodic table and the size of the cations involved. Let's break down the analysis step by step.

### Step 1: Understand Bicarbonate Stability
- **Bicarbonates**: The thermal stability of bicarbonates increases down the group in the alkali metals (Li, Na, K, Rb, Cs).
- **Reason**: As we move down the group, the size of the cation increases, which stabilizes the bicarbonate ion.

### Step 2: Analyze Peroxide Stability
- **Peroxides**: The stability of peroxides also increases with the increase in cation size.
- **Reason**: A larger cation can stabilize a larger anion (the peroxide ion, O2^2-). Thus, the order of stability would be BaO2 > SrO2 > CaO2.

### Step 3: Evaluate Cation Charge and Ionic Character
- **Cation Charge**: The stability of ionic compounds is affected by the charge of the cation. As the charge increases, the ionic character decreases, leading to decreased thermal stability.
- **Example**: For sulfate compounds, the order of thermal stability would be Na2SO4 > MgSO4 > Al2(SO4)3, as sodium has a +1 charge and is the least ionic, while aluminum has a +3 charge and is the most ionic.

### Step 4: Group 14 Elements and Oxidation States
- **Group 14**: The stability of the +4 oxidation state decreases down the group due to the inert pair effect.
- **Reason**: The s-electrons become less involved in bonding as we move down the group, leading to increased stability in the +2 oxidation state compared to the +4 state.
- **Example**: The order of stability would be CCl4 > SiCl4 > GeCl4 > SnCl4.

### Conclusion
After analyzing the thermal stability of bicarbonates, peroxides, cation charge effects, and group 14 elements, we find that the incorrect order is related to the stability of peroxides, specifically the order of BaO2, SrO2, and CaO2. The correct order should reflect that BaO2 is more stable than SrO2 and CaO2, making option B the incorrect order.

### Final Answer
The incorrect order of thermal stability is **option B**.

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