Rockets and jet planes fly on the basis of which of the folowing options :-​ ​​

1. Newton's third law
2. Conservation of linear momentum
3. Both (1.) and (2.) options

answer is (3.) 
but how conservation of linear momentum is applicable

in a rocket, the hot gases produced by rapid burning of fuel rush out through the tail nozzle of the rocket rush out at very high velocity hence its momentum will be very , but before the rocket starts to propel the total momentum of the system was zero , hence to conserve the momentum after the rocket started to propel , it rises up with a momentum equal to that  of the gases which rushed out. in this way, the rocket works on the principle of law of conservation of linear momentum.