Question

as the fuel in a rocket ignites, the force of gas expansion and explosion pushes out the back of the rocket and pushes the rocket forward.

Explanation:

Newton's 3rd Law of Motion states that for every action, there is an equal and opposite reaction. In the case of a rocket, the action is the force of gas expansion and explosion pushing out the back of the rocket, and the reaction is the force that pushes the rocket forward.

Answer:

Newton's 3rd Law of Motion