Answer:

Introduction: Torque is a measure of the rotational force acting on a body. It is defined as the product of the force and the perpendicular distance from the axis of rotation to the line of action of the force. The torque acting on a body about the centre of mass due to normal reaction can be zero, non-zero, or may vary depending on the body's state.

Must be zero: The torque acting on a body about the centre of mass due to normal reaction must be zero if the body is in equilibrium. In an equilibrium state, the net force acting on the body is zero, and the torque acting on the body is also zero. Therefore, the torque acting on a stationary body due to normal reaction must be zero.

Must be non-zero: The torque acting on a body about the centre of mass due to normal reaction must be non-zero if the body is accelerating. When a body is accelerating, there is a net force acting on it. The normal reaction force acts perpendicular to the surface, and the distance between the line of action of the force and the axis of rotation is non-zero. Therefore, the torque acting on a moving body due to normal reaction must be non-zero.

May be non-zero on stationary or moving body: The torque acting on a body about the centre of mass due to normal reaction may be non-zero on a stationary or moving body if the force acting on the body is not perpendicular to the surface. In such a case, the normal reaction force will have a non-zero component perpendicular to the surface, and the torque acting on the body will also be non-zero.

Conclusion: In summary, the torque acting on a body about the centre of mass due to normal reaction can be zero, non-zero, or may vary depending on the body's state. It is important to understand the concept of torque and its relation to the normal reaction force to solve problems related to rotational motion.

The answer is 1) cuz the centre of mass is the point where the net force is zero,since force is equal to torque the net torque should be zero