Correct option is (a) Zero
The correct answer should be zero. When a bar magnet or magnetic dipole is placed in a uniform magnetic field, it will not experience only force, but it is bound to experience a torque.
This torque will align the dipole moment of the bar magnet to align along the direction of magnetic field. However, if a bar magnet is placed in a non-uniform magnetic field, then it will be subjected to a force and torque both.
