Which of the following situations is NOT an example of action and reaction forces?

The correct option is: A ball thrown upward comes back down due to the pull of gravity.

Explanation:
Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. Action and reaction forces always occur in pairs, act on two different objects simultaneously, and are equal in magnitude but opposite in direction.

Let us analyze each situation to understand why they represent or do not represent action-reaction force pairs:
1. A swimmer pushing water backwards: When a swimmer pushes the water backward (action force), the water exerts an equal and opposite force pushing the swimmer forward (reaction force). This is a clear example of action and reaction.
2. A bat hitting a cricket ball: The bat exerts a force on the cricket ball to hit it (action force), and the ball exerts an equal and opposite force back onto the bat (reaction force), which can be felt by the person holding the bat. This is an example of action and reaction.
3. A rocket launching upwards: The rocket's engines expel hot exhaust gases downward (action force), and these gases exert an equal and opposite upward thrust on the rocket (reaction force), propelling it into space. This is also an example of action and reaction.

4. A ball thrown upward comes back down due to the pull of gravity: When a ball falls back down, it is accelerating downward due to the external force of Earth's gravity acting on it. While a gravitational action-reaction pair does technically exist (the Earth pulls the ball down, and the ball pulls the Earth up with an equal force), the scenario of a ball falling back down is described from the perspective of a single force (gravity) acting on a single object (the ball) causing it to fall. Unlike the other examples, which describe immediate, active contact force-pair interactions causing motion, this situation illustrates Newton's Second Law of Motion:

$F=ma$

Here, gravity acts as an unbalanced force causing the ball to accelerate downward, rather than illustrating a practical example of action-reaction pairs in everyday contact forces.