A body is performing circular motion. An observer O1 is sitting at the centre of the circle and another observer O2 is sitting on the body. The centrifugal force is experienced by the observer.

The correct answer is O₂ only.

To understand why, we need to analyze the frames of reference of both observers:
1. Observer O₁ (at the centre of the circle): This observer is at a fixed, non-rotating position at the center of the circular trajectory. Thus, observer O₁ is in an inertial frame of reference. In an inertial frame, only real forces (such as tension, gravity, or friction) act on objects. Pseudo forces, like the centrifugal force, do not exist in inertial frames. Therefore, O₁ does not experience centrifugal force.
2. Observer O₂ (on the body performing circular motion): This observer is sitting on the rotating body. Because the body is constantly changing its direction of motion, it is undergoing acceleration directed toward the center (centripetal acceleration). This makes the frame of reference of observer O₂ a non-inertial (rotating) frame of reference. In any non-inertial frame, a pseudo force must be applied to explain the mechanics of objects. This radially outward pseudo force is the centrifugal force. Therefore, observer O₂ experiences the centrifugal force.

Consequently, the centrifugal force is experienced by observer O₂ only.