Question

Name the principle on which a rocket works

Answer 1

A rocket works on the Newton's third law of motion which states that   "For every action, there is an equal and opposite reaction".
So when the exhaust gases of the rocket fire backwards , it receives an equal push from the from the atmosphere which helps it move forward.

Answer 2

When a rocket lifts up, burning fuel gases are ejected in a backwards direction which has both mass and velocity, providing momentum to the rocket to take off.

Complete step-by-step answer:

Rocket works on the principle of conservation of momentum. Rocket ejaculates gases in a backward direction which creates a momentum of the gases backwards and thus by conservation of momentum, the rocket gets momentum in the forward direction making it move forward.

Thus the rocket works on the principle of conservation of linear momentum.