Question

why smoke molecule goes upward against gravity

Answer 1

1) It's precisely because of gravity that they go upwards.
2) kinetic energy increases and distance between molecules increases correspondingly, which makes gas rare and less denser.

Answer 2

· The heated air is less dense than the surrounding cooler air, and so the cooler air "squeezes out" the hot air, which moves upward. As the hot air moves upward, so does some of the still-burning material, resulting in a flame that flickers upward, away from gravity.