Which of the following statements is not correct about magnetic behaviour of substances ?

Options

A. Diamagneti substances are repelled by an applied magnetic field.
B. Paramagnetic substances are attracted by and applied magnetic field.
C. Magnetic moment of n unpaired electrons is given by `mu=sqrt(n(n-2))` B.M.
D. Magnetic moment increases as the number of unpaired electrons increases.

Explanation

To determine which statement is not correct about the magnetic behavior of substances, we will analyze each statement one by one.

### Step 1: Analyze the Statements

1. **Diamagnetic substances are repelled by an applied magnetic field.**
- **Explanation:** Diamagnetic substances have all their electrons paired. When an external magnetic field is applied, they are weakly repelled. This statement is correct.

2. **Paramagnetic substances are attracted by an applied magnetic field.**
- **Explanation:** Paramagnetic substances contain unpaired electrons, which means they have a net magnetic moment. They are attracted to an external magnetic field. This statement is also correct.

3. **Magnetic moment of unpaired electrons is given by μ = √(n(n-2)) Bohr magneton.**
- **Explanation:** The correct formula for calculating the magnetic moment (μ) of substances with unpaired electrons is μ = √(n(n + 2)) Bohr magneton, where n is the number of unpaired electrons. This statement is incorrect.

4. **Magnetic moment increases as the number of unpaired electrons increases.**
- **Explanation:** As the number of unpaired electrons increases, the magnetic moment also increases. This statement is correct.

### Step 2: Identify the Incorrect Statement
From the analysis above, we can conclude that the third statement is not correct. The correct formula should include (n + 2) instead of (n - 2).

### Final Answer
The statement that is not correct about the magnetic behavior of substances is:
**3. Magnetic moment of unpaired electrons is given by μ = √(n(n-2)) Bohr magneton.**

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