Which of the following is incorrect ?

Options

A. Diamagnetic property is because of the induced dipole moment due to change in the orbital motion of electrons in atoms by the applied field
B. Paramagnetic property is primarily because of the unpaired electrons present in the atoms and molecules
C. Ferromagnetism arises due to spin-orbit interaction , due to which material gets divided into small regions called domains
D. None of these

Answer

To determine which of the statements regarding magnetic properties is incorrect, let's analyze each option step by step:

### Step 1: Analyze Option 1
**Statement**: "Di-magnetic property is because of induced dipole moment due to change in the orbital motion of the electrons in atoms by the applied field."

**Analysis**: This statement is correct. Diamagnetism occurs due to the induced dipole moments that arise from changes in the orbital motion of electrons when an external magnetic field is applied. The induced dipole moments oppose the applied magnetic field, resulting in a negative susceptibility.

### Step 2: Analyze Option 2
**Statement**: "The paramagnetic property is primarily because of the unpaired electrons present in the atoms and the molecules."

**Analysis**: This statement is also correct. Paramagnetism is indeed due to the presence of unpaired electrons in the atoms or molecules. These unpaired electrons contribute to a net magnetic moment, which aligns with an external magnetic field, resulting in positive susceptibility.

### Step 3: Analyze Option 3
**Statement**: "Ferromagnetism arises due to spin-orbit interaction due to which material gets divided into small regions or the domains."

**Analysis**: This statement is incorrect. While ferromagnetism does involve interactions between electron spins, it is primarily due to exchange interactions rather than spin-orbit coupling. The phenomenon of ferromagnetism leads to the formation of magnetic domains where the magnetic moments are aligned in the same direction, but the cause is not correctly attributed to spin-orbit interaction.

### Step 4: Analyze Option 4
**Statement**: "None of these."

**Analysis**: Since we have identified that Option 3 is incorrect, this option is not applicable.

### Conclusion
The incorrect statement is **Option 3**: "Ferromagnetism arises due to spin-orbit interaction due to which material gets divided into small regions or the domains."