When a boy comes running and sits in a rotating platform, the angular momentum is conserved. This is because the rotating platform undergoes rotational motion and in rotational motion, angular momentum is always conserved due to zero net torque acting on it.

Conservation of Angular Momentum:

Angular momentum is a physical quantity that describes the rotational motion of an object. It is defined as the product of the moment of inertia and the angular velocity of an object. When a boy comes running and sits on a rotating platform, the angular momentum of the system is conserved.

Explanation:

1. Initial Angular Momentum:
Before the boy sits on the rotating platform, the system consists of the platform only. As the platform is already rotating, it possesses angular momentum. The initial angular momentum of the system is given by the product of the moment of inertia of the platform and its angular velocity.

2. Final Angular Momentum:
When the boy sits on the platform, his mass gets added to the system, but angular momentum is still conserved. The moment of inertia of the system increases due to the addition of the boy's mass. To conserve angular momentum, the angular velocity of the system decreases.

3. Conservation of Angular Momentum:
According to the law of conservation of angular momentum, the total angular momentum of an isolated system remains constant if no external torques act on it. In this case, the system of the boy and the rotating platform is considered an isolated system as no external torques are applied.

4. Explanation of Options:
a) Linear Momentum: Linear momentum is the product of mass and linear velocity. It is not conserved in this scenario as the boy's mass is added to the system, resulting in a change in linear momentum.
b) Kinetic Energy: Kinetic energy is the energy possessed by an object due to its motion. It is not conserved in this scenario as the angular velocity of the system changes, resulting in a change in kinetic energy.
c) Angular Momentum: Angular momentum is conserved in this scenario as explained above. The addition of the boy's mass increases the moment of inertia, causing the angular velocity to decrease while conserving the total angular momentum of the system.
d) None of the above: The correct answer is not "None of the above" because angular momentum is indeed conserved in this scenario.

In conclusion, when a boy comes running and sits on a rotating platform, the conservation of angular momentum occurs as the moment of inertia of the system increases due to the addition of the boy's mass, resulting in a decrease in angular velocity while keeping the total angular momentum constant.