Answer: (a) A satellite launch vehicle (launcher) such as PSLV/GSLV works like it; (b) Newton’s third law of motion.
(a) The Diwali rocket is a small model of a launcher, i.e. a satellite launch vehicle; ISRO’s launchers are PSLV and GSLV.
(b) It works on Newton’s third law of motion (law of conservation of momentum): hot gases from the burning fuel are pushed out backwards with great force (action), and the gases push the rocket forwards with an equal and opposite force (reaction).