Which of the following statements is not true ?

Options

A. Paramagnetic substances are weakly attacted 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 determine which statement is not true regarding paramagnetic and ferromagnetic substances, we can analyze the provided statements step by step.

### Step 1: Analyze the First Statement
**Statement:** "Paramagnetic substances are weakly attracted by magnetic field."
- **Explanation:** This statement is true. Paramagnetic substances do exhibit weak attraction to magnetic fields due to the presence of unpaired electrons that align with the magnetic field.

### Step 2: Analyze the Second Statement
**Statement:** "Ferromagnetic substances cannot be magnetized permanently."
- **Explanation:** This statement is false. Ferromagnetic substances can indeed be magnetized permanently. They have a strong attraction to magnetic fields and can retain their magnetization even after the external magnetic field is removed.

### Step 3: Analyze the Third Statement
**Statement:** "Paramagnetic substances are anti-ferromagnetic and have an anti-parallel arrangement of spins."
- **Explanation:** This statement is misleading. While it is true that anti-ferromagnetic materials have spins that are anti-parallel, paramagnetic substances do not exhibit this behavior. Instead, paramagnetic materials have unpaired electrons that align with the magnetic field but do not have a fixed arrangement like anti-ferromagnetic materials.

### Conclusion
Based on the analysis, the statement that is not true is: **"Ferromagnetic substances cannot be magnetized permanently."**

### Summary of Findings
1. **True:** Paramagnetic substances are weakly attracted by magnetic fields.
2. **False:** Ferromagnetic substances cannot be magnetized permanently.
3. **Misleading:** Paramagnetic substances are anti-ferromagnetic and have an anti-parallel arrangement of spins.