Question

Why does a gas exert pressure ?

Answer 1

Heyy 
____________________________________________________
As You know pressure is directly proportional to Mass of the object 
As gas formed of small particles which have having mass in it so gases exert pressure 
______________________________________________________________

Answer 2

<>The particles of Gas are moving constantly in all directions
<>While they move , they come in contact with other particles and collide with each other
<>So , they also exerts pressure .