Which of the following is not correct ?

Options

A. `3 O_2 overset ("Sileny electric") underset ("Discharge") hArr 2 O_3 , Delta H = -284.5 kJ`.
B. Ozone undergoes addition reaction with unsaturated carbon compounds
C. Sodium thiosulphate reacts with `I_2` to form sodium tetrathionate and sodium iodide.
D. Ozone oxidises lead sulphide to lead sulphate

Explanation

To determine which of the following statements is not correct, we will analyze each statement one by one:

1. **Statement 1**: O2 is converted to O3 with an enthalpy change of -284.5 kJ.
- **Analysis**: The formation of ozone (O3) from oxygen (O2) is an endothermic reaction, meaning it requires energy input (typically from electric discharge). In an endothermic reaction, the enthalpy change (ΔH) is positive, not negative. Therefore, stating that ΔH is -284.5 kJ is incorrect.
- **Conclusion**: This statement is **not correct**.

2. **Statement 2**: Ozone undergoes addition reactions with unsaturated compounds.
- **Analysis**: Ozone (O3) can react with unsaturated compounds like alkenes and alkynes through a process known as ozonolysis. This reaction involves the addition of ozone across the double or triple bonds of these compounds, leading to the formation of various products.
- **Conclusion**: This statement is **correct**.

3. **Statement 3**: Sodium thiosulfate reacts with iodine to form sodium tetrathionate and sodium iodide.
- **Analysis**: When sodium thiosulfate (Na2S2O3) reacts with iodine (I2), it indeed produces sodium tetrathionate (Na2S4O6) and sodium iodide (NaI). This is a well-known reaction in chemistry.
- **Conclusion**: This statement is **correct**.

4. **Statement 4**: Ozone oxidizes lead sulfide to lead sulfate.
- **Analysis**: Ozone can oxidize lead sulfide (PbS) to lead sulfate (PbSO4). This reaction is also known and can be represented with the formation of oxygen as a by-product. The color change from black (PbS) to white (PbSO4) is also notable.
- **Conclusion**: This statement is **correct**.

**Final Conclusion**: The only statement that is not correct is **Statement 1**.

### Summary of Steps:
1. Analyze the first statement regarding the enthalpy of ozone formation.
2. Confirm the correctness of the second statement about ozone's reactions with unsaturated compounds.
3. Validate the third statement regarding sodium thiosulfate's reaction with iodine.
4. Assess the fourth statement about ozone oxidizing lead sulfide.