A jet engine works on the principle of conservation of

The correct option is D

Linear momentum

The explanation for the correct option

1. In a jet engine, a large volume of gases is produced by fuel combustion.
2. These gases are allowed to be released from the back of the jet engine with high velocity.
3. Due to the very high speed or velocity, the backward rushing gases have a large momentum.
4. They impart an equal and opposite momentum to the jet engine due to which the jet engine moves forward with a great speed.
5. Therefore, the conservation of the linear momentum is the main principle behind a jet engine.

The explanation for the incorrect options

1. The principle of a jet engine can not be the conservation of mass alone, as the fuel is burning into gas, which is giving the jet a high amount of speed.
2. Thus, the velocity needs to be considered too.
3. Due to that same reason, the conservation of energy and flow can not be the principle behind a jet engine.

Hence, the correct option is (D).