The correct answer to the question is option 1: linear momentum.

Linear momentum is defined as the product of an object`s mass and its velocity. According to the principle of conservation of linear momentum, the total linear momentum of an isolated system remains constant provided no external forces act on it.

In the case of a jet engine, the working principle is based on Newton`s third law of motion, which states that for every action, there is an equal and opposite reaction. When fuel is burned in the combustion chamber of a jet engine, it produces a high-velocity jet of exhaust gases. As these gases are expelled, they produce a backward thrust force, which in turn propels the jet engine forward.

By Newton`s third law, the force exerted by the exhaust gases on the engine is equal in magnitude and opposite in direction to the force exerted by the engine on the gases. This produces a change in momentum, and the conservation of linear momentum ensures that the total momentum of the system remains constant.

Therefore, a jet engine works on the principle of conservation of linear momentum.