An inflated air balloon collapses when pricked with a pin. Which property of gaseous state is shown by this?

This is because of the process named diffusion. 
Diffusion means spreading out from a non-concentrated area to a concentrated area.

can you please tell that why it happens... 

particles of gas are continuously moving.therefore they hav high kinetic energy.they thus strike the walls of the inflated air balloon or any othe vessel,and when there is a hole in the balloon,the particles move out of it

Because of the small area of the needle and the force that is exerted on the balloon. The pressure inside the balloon that was previously more, finally can diffuse into the room. Since the air canot all escape from the needle prick it bursts to equal the pressure. And while it gets bursted, the air diffuses around! 

Hope it clears u! :)

particles of gas are continuously moving.therefore they have high kinetic energy and strike the walls of the container in which they are kept.therefore when there is a hole in the container,the charged particles move outside

thank you...