Explanation:

- Jet engines primarily function based on the principle of conservation of linear momentum.

- They eject high-speed gases backward, generating forward thrust as per Newton’s third law of motion.

- Correct Answer: Linear momentum

- Conservation of heat is not the direct operational principle.

- Jet engines do involve thermodynamics but primarily focus on energy conversion, not heat conservation.

- Conservation of mass relates to how fuel and air are handled in the engine.

- While important, it doesn’t directly explain the thrust mechanism.

- Conservation of angular momentum is relevant in contexts like rotation of turbines.

- It’s not the core principle for explaining thrust.