The question asks about the behavior of a compass needle when placed in a uniform magnetic field, specifically why it oscillates around its equilibrium position. The correct answer is that the compass needle experiences a torque. Let's understand why this is the case and rule out the other options.

1. **Understanding Torque in Magnetic Fields:**

A compass needle is essentially a small magnet. When placed in a magnetic field, it aligns itself with the field due to the force acting on its magnetic dipole moment. If the initial position of the needle is not aligned with the magnetic field, the magnetic field exerts a torque on the needle.

The torque (\tau) experienced by a magnetic dipole in a magnetic field is given by the formula:

\tau = \mu \times B

where:

• \mu = magnetic moment of the needle
• B = magnetic field strength

The torque tends to rotate the needle until it aligns with the magnetic field lines, causing it to oscillate about the equilibrium position.

2. **Reasoning and Ruling Out Other Options:**

• **Option: It experiences a net force** - This is incorrect because a uniform magnetic field exerts torque, not a translational force, on a magnetic dipole. A net force would cause linear motion, not oscillation.
• **Option: It gains energy from the field continuously** - This is incorrect. The compass needle does not gain energy continuously from the field. The oscillation is due to the initial torque and subsequent restoration forces as it tries to align with the field.
• **Option: The magnetic field is non-uniform** - This is incorrect. The question specifically states a uniform magnetic field. In a non-uniform field, both torque and force can be exerted, but the question specifies uniformity.

3. **Conclusion:**

The correct answer is that "It experiences a torque". The needle oscillates because of the torque acting on it, trying to align with the magnetic field direction. This is the typical behavior of a magnetic dipole in a uniform magnetic field.