A magnetic needle is kept in a non-uniform magnetic field. It experiences

A magnetic needle is simply a magnetic dipole of magnetic moment $$\vec m$$ mounted so that it can freely rotate and, if the pivot has negligible friction, can also translate when an external force acts.

For a magnetic dipole placed in an external magnetic field $$\vec B(\vec r)$$ two separate interactions must be analysed:

1. Torque on a dipole
The torque acting on a magnetic dipole is given by the vector product
$$\vec \tau = \vec m \times \vec B$$
This formula is valid irrespective of whether the field is uniform or non-uniform. Hence a torque will certainly act unless $$\vec m$$ happens to be parallel or antiparallel to the local field.

2. Net translational force on a dipole
The potential energy of a dipole in a magnetic field is
$$U = -\vec m \cdot \vec B(\vec r)$$
The net force is the negative gradient of this energy:
$$\vec F = -\nabla U = \nabla(\vec m \cdot \vec B)$$
If the field is uniform, $$\vec B$$ is the same at every point, so $$\nabla(\vec m \cdot \vec B)=0$$ and no net force appears. If, however, the field is non-uniform, $$\vec B$$ varies with position, giving a non-zero gradient and therefore a non-zero net force.

Because the question explicitly states that the magnetic field is non-uniform, both interactions occur:

• A rotational effect (torque) tries to align the needle with the local field direction.
• A translational effect (force) tends to pull the needle toward the region where $$\vec m\cdot\vec B$$ is larger (typically where the field is stronger).

Therefore the magnetic needle experiences both a torque and a force.

Option C which is: a force and a torque