The correct answer is option 2: The floor exerts a force on the ball during the impact. When a ball drops onto the floor, it bounces because of the force that the floor exerts on the ball.

Option 1 states that Newton`s third law implies that for every action (drop), there is a reaction (bounce). This is a valid statement, as Newton`s third law states that every action has an equal and opposite reaction. However, it does not directly explain why the ball bounces when it hits the floor.

Option 3 suggests that the floor is perfectly rigid. While this may be true in some cases, the rigidity of the floor does not directly impact the bouncing of the ball.

Option 4 states that the floor heats up on impact. This is not a valid explanation for why the ball bounces. The heating of the floor does not play a role in the ball`s rebound.

In conclusion, the correct answer is option 2 because the floor exerts a force on the ball during the impact, causing it to bounce.