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

Explanation

To determine which statement is not true among the options given, we will analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** Paramagnetic substances are weakly attracted by magnetic fields.

**Explanation:**
Paramagnetic substances have unpaired electrons, which means they have a net magnetic moment. When placed in a magnetic field, these substances tend to align with the field, resulting in a weak attraction. Therefore, this statement is **true**.

### Step 2: Analyze the Second Statement
**Statement:** Ferromagnetic substances cannot be magnetized permanently.

**Explanation:**
Ferromagnetic substances, such as iron, can be magnetized permanently. They have a strong response to magnetic fields and can retain their magnetization even after the external field is removed. Thus, this statement is **not true**.

### Step 3: Analyze the Third Statement
**Statement:** The domains in anti-ferromagnetic substances are oppositely oriented with respect to each other.

**Explanation:**
In anti-ferromagnetic materials, the magnetic moments of adjacent atoms or ions align in opposite directions, effectively canceling each other out. This means that the domains are indeed oppositely oriented. Therefore, this statement is **true**.

### Step 4: Analyze the Fourth Statement
**Statement:** The pairing of electrons cancels their magnetic moments in diamagnetic substances.

**Explanation:**
Diamagnetic substances have all their electrons paired. The opposite spins of the paired electrons cancel each other’s magnetic moments, resulting in no net magnetic moment. Therefore, this statement is **true**.

### Conclusion
After analyzing all the statements, we find that the second statement is the only one that is not true.

**Final Answer:** The statement that is not true is: "Ferromagnetic substances cannot be magnetized permanently."

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