Which of the following statements is not true ?

Options

A. Paramagnetic substances are weakly attracted by magnetic field
B. Ferromagnetic substances cannot be magnetised permanently
C. The domains in antiferromagnetic substances are oppositely oriented with respect to each other
D. Pairing of electrons cancels their magnetic moment in the diamagnetic substances .

Answer

To solve the question "Which of the following statements is not true?", we need to analyze each statement related to magnetic properties of substances.

### Step-by-Step Solution:

1. **Understand Paramagnetic Substances**:
- Paramagnetic substances have at least one unpaired electron.
- They are weakly attracted by an external magnetic field.
- **Statement**: "Paramagnetic substances are weakly attracted by magnetic field."
- **Evaluation**: This statement is true.

2. **Understand Ferromagnetic Substances**:
- Ferromagnetic substances can be magnetized permanently.
- When placed in an external magnetic field, they retain their magnetization even after the field is removed.
- **Statement**: "Ferromagnetic substances can't be magnetized permanently."
- **Evaluation**: This statement is false. Ferromagnetic substances can indeed be magnetized permanently.

3. **Understand Antiferromagnetic Substances**:
- In antiferromagnetic substances, the magnetic moments of the atoms or ions are aligned in opposite directions, canceling each other out.
- This leads to a net magnetic moment of zero.
- **Statement**: "The domains in antiferromagnetic substances are oppositely oriented with respect to each other."
- **Evaluation**: This statement is true.

4. **Understand Diamagnetic Substances**:
- Diamagnetic substances have all their electrons paired.
- The pairing of electrons results in a net magnetic moment of zero because the magnetic moments cancel each other out.
- **Statement**: "Pairing of electrons cancels their magnetic moment in the diamagnetic substances."
- **Evaluation**: This statement is true.

5. **Conclusion**:
- The only statement that is not true is regarding ferromagnetic substances: "Ferromagnetic substances can't be magnetized permanently." This is incorrect because ferromagnetic substances can indeed be magnetized permanently.

### Final Answer:
The statement that is not true is: **"Ferromagnetic substances can't be magnetized permanently."**

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