Which law describes that for every action, there is an equal and opposite reaction?

The principle that states for every action, there is an equal and opposite reaction is encapsulated in Newton's Third Law of Motion. This law highlights the interaction between two bodies: when one body exerts a force on a second body, the second body simultaneously exerts a force of equal magnitude but in the opposite direction on the first body. This fundamental concept is crucial in understanding how forces work in pairs and is evident in various real-world scenarios, such as how a rocket propels itself forward by expelling gas backward.

The focus of Newton's Third Law is on the forces that two objects exert on each other, emphasizing that they are always equal and opposite. This characteristic is essential in fields ranging from physics to engineering, as it underlies the functioning of numerous machines and systems. Therefore, the correct answer clearly reflects this fundamental understanding of motion and forces.