Which statement is not correct

Options

A. Potassium permanganate is a powerful oxidising substance
B. Potassium permanganate is a weaker oxidising substance than potassium dichromate
C. Potassium permanganate is a stronger oxidising substance than potassium dichromate
D. Potassium dichromate oxidises a secondary alcohol into a ketone

Explanation

To determine which statement is not correct regarding potassium permanganate and potassium dichromate, we will analyze the statements one by one.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Potassium permanganate (KMnO4) is known as a strong oxidizing agent.
- Potassium dichromate (K2Cr2O7) is also an oxidizing agent, but it is generally considered weaker than potassium permanganate.

2. **Evaluate the Statements**:
- **Statement 1**: "Potassium permanganate is a powerful oxidizing substance."
- This statement is true. Potassium permanganate is indeed a strong oxidizing agent.

- **Statement 2**: "Potassium permanganate is a weaker oxidizing substance than potassium dichromate."
- This statement is false. Potassium permanganate is stronger than potassium dichromate, making this statement incorrect.

- **Statement 3**: "Potassium permanganate is a stronger oxidizing substance than potassium dichromate."
- This statement is true. As established, KMnO4 is a stronger oxidizing agent compared to K2Cr2O7.

- **Statement 4**: "Potassium dichromate oxidizes a secondary alcohol to a ketone."
- This statement is true. Potassium dichromate can oxidize secondary alcohols to ketones.

3. **Conclusion**:
- The statement that is not correct is **Statement 2**: "Potassium permanganate is a weaker oxidizing substance than potassium dichromate."

### Final Answer:
The statement that is not correct is: **Potassium permanganate is a weaker oxidizing substance than potassium dichromate.**

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