`FeSO_(4).7H_(2)O` (Green vitriol) salt on thermal decomposition does not produce:

Options

A. `SO_(2)`
B. `O_(2)`
C. `SO_(3)`
D. `H_(2)O` vapour

Explanation

To solve the question regarding the thermal decomposition of `FeSO4.7H2O` (Green vitriol), we will analyze the decomposition process step by step.

### Step-by-Step Solution:

1. **Understanding the Compound**:
- The compound in question is `FeSO4.7H2O`, which is ferrous sulfate heptahydrate. It contains 7 molecules of water of crystallization.

2. **Heating the Compound**:
- When `FeSO4.7H2O` is heated, the first step involves the loss of water. The water of crystallization evaporates, leading to the formation of anhydrous ferrous sulfate (`FeSO4`).

3. **Decomposition of Anhydrous Ferrous Sulfate**:
- Upon further heating, the anhydrous ferrous sulfate (`FeSO4`) undergoes thermal decomposition. The decomposition reaction can be represented as:
\[ 2 \text{FeSO}_4 \rightarrow \text{Fe}_2\text{O}_3 + \text{SO}_2 + \text{SO}_3 \]
- In this reaction, we can observe that the products formed are:
- Ferric oxide (`Fe2O3`), which is a solid.
- Sulfur dioxide (`SO2`), which is a gas.
- Sulfur trioxide (`SO3`), which is also a gas.

4. **Identifying the Products**:
- From the decomposition reaction, we see that `SO2` and `SO3` are produced. However, we need to determine which of the given options is not produced during this reaction.

5. **Analyzing the Options**:
- The options provided are:
1. SO2
2. O2
3. SO3
4. S2O vapor
- From our analysis, we see that `SO2` and `SO3` are produced in the reaction. The compound `S2O` vapor is not a typical product of this reaction, but it is not explicitly mentioned in the thermal decomposition of `FeSO4`.

6. **Conclusion**:
- The only gas that is not produced during the thermal decomposition of `FeSO4.7H2O` is `O2`. Therefore, the correct answer is:
- **O2** is not produced in this reaction.

### Final Answer:
**O2** is not produced during the thermal decomposition of `FeSO4.7H2O`.