Pick out the incorrect statement

Options

A. In ferromagnetic material , all the magnetic moments are aligned in the same direction
B. In anti - ferromagnetic material , magnetic moments are aligned in parallel and anti - parallel directions in equal numbers
C. In ferrimagnetism, magnetic moments moments are aligned in parallel and anti - parallel direction in unequal number
D. Paramagnetism of a substance increases at elevated temperature

Answer

To solve the question of identifying the incorrect statement among the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Evaluate Statement 1**:
- The statement claims that in ferromagnetic materials, all the magnetic moments are aligned in the same direction.
- **Analysis**: This is true. Ferromagnetic materials exhibit a strong magnetic alignment where all magnetic moments align in the same direction, resulting in a net magnetic moment.

2. **Evaluate Statement 2**:
- The statement claims that in antiferromagnetic materials, magnetic moments are aligned in parallel and antiparallel directions in equal numbers.
- **Analysis**: This is also true. In antiferromagnetic materials, the magnetic moments align in opposite directions (antiparallel) in equal quantities, leading to a cancellation of the net magnetic moment.

3. **Evaluate Statement 3**:
- The statement claims that in ferrimagnetism, magnetic moments are aligned in parallel and antiparallel directions in unequal numbers.
- **Analysis**: This statement is true as well. Ferrimagnetic materials have magnetic moments that align in opposite directions but are not equal in magnitude, resulting in a net magnetic moment.

4. **Evaluate Statement 4**:
- The statement claims that the paramagnetism of a substance increases at elevated temperatures.
- **Analysis**: This statement is false. As temperature increases, thermal agitation causes random motion, which disrupts the alignment of magnetic dipoles. This leads to a decrease in paramagnetism, not an increase.

### Conclusion:
The incorrect statement is **Statement 4**: "Paramagnetism of a substance increases at elevated temperature."

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