Assertion: Magnetic force between two short magnets, when they are co-axial follows inverse square law of distance.
Reason: The magnetic forces between two poles do not follow inverse square law of distance.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true and reason is not the correct explanation of assertion.
C. If assertion is ture but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the given statements, we will evaluate both the assertion and the reason separately.

### Step 1: Understanding the Assertion
The assertion states that the magnetic force between two short magnets, when they are co-axial, follows the inverse square law of distance.

- **Magnetic Force Between Co-Axial Magnets**: The formula for the magnetic force \( F \) between two short magnets when they are aligned along the same axis is given by:
\[ F = \frac{B^2}{2\mu} \cdot A \]
where \( B \) is the magnetic induction in the gap between the magnets, \( \mu \) is the permeability of free space, and \( A \) is the contact surface area.

- **Conclusion on Assertion**: This formula does not show that the force varies with the square of the distance \( R \). Therefore, the assertion is **incorrect**.

### Step 2: Understanding the Reason
The reason states that the magnetic forces between two poles do not follow the inverse square law of distance.

- **Magnetic Force Between Poles**: The force \( F \) between two magnetic poles can be expressed as:
\[ F = \frac{\mu Q_1 Q_2}{4\pi R^2} \]
where \( Q_1 \) and \( Q_2 \) are the strengths of the magnetic poles and \( R \) is the distance between them.

- **Conclusion on Reason**: This formula indicates that the force between two magnetic poles does indeed follow the inverse square law of distance. Therefore, the reason is also **incorrect**.

### Final Conclusion
Both the assertion and the reason are incorrect.