Question

a bullet fired from a gun is more dangerous then an air molecule hitting a person thought Both bullet and air molecule are moving with same velocity explain

Answer 1

It is all because of the momentum. Mass of the air compared to the bullet is very small. When the bullet is shot with a great speed the momentum carried by it is large. That is why it harms the person while an air molecule doesn't.
Momentum = mass × velocity

Answer 2

A crowd of Libyans fired guns in the airand chanted slogans in support of Muammar Qaddafi at a rally in the city of Sirte on Monday. Isn't it kind of dangerous to shoot bullets into the sky?

Yes ... well, probably ... maybe ... it kind of depends. The Explainer is far from being the first to ask this question. Everyone from the U.S. military to The Straight Dope's Cecil Adams has probed the lethality of falling bullets. That includes forensic scientists, cardio-thoracic surgeons, and the hosts of the Discovery Channel's Mythbusters—which devoted nearly a whole episode to the matter.