Assertion:  When a magnetic dipole is placed in a non uniform magnetic field, only a torque acts on the dipole. 

Reason:  Force would act on dipole if magnetic field is uniform.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false.

• If both assertion and reason are false.

D.

If both assertion and reason are false.

When dipole is placed uniformly electric field and dipole vector direction is not parallel to field direction, each charge of dipole experiences a force. The magnitude of the two forces are equal but opposite in direction. These equal and unlike give rise to couple. This couple gives a torque to dipole, which rotates the dipole and makes it align to the direction of a field. Once the dipole is aligned in the direction of field, torque vanishes ( r × F will be zero, if r and F are in same direction). Once the dipole is aligned to electric field, the net force will be zero because they are in opposite direction. Hence in uniform field dipole experiences only torque.

When a dipole is placed in non-uniform field, there will be torque as explained above. But once the dipole is aligned to field direction, the forces acting on the charges are not same. Hence there will be a net force acting on the dipole in the direction of magnetic field. Hence in non-uniform field, electric dipole experiences both torque and force.