The law of motion that states forces always act in equal but opposite pairs is Newton's Third Law of Motion.

Here's a breakdown:

* Newton's Third Law: For every action, there is an equal and opposite reaction.

* What it means: When one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object.

* Examples:

* When you push against a wall, the wall pushes back on you with the same force.

* When a rocket launches, it expels hot gas downwards, and the gas pushes back on the rocket, propelling it upwards.

* When you jump, your feet push down on the ground, and the ground pushes back up on your feet.

Let me know if you have any other questions about Newton's Laws of Motion!