Question

how will you demonstrate that air has some pressure ?

Answer 1

Take an empty soda bottle with minimum thickness open the cap. Hold it in the mouth and suck all the air with a vacuum pump. What happens to the bottle? The shape of the bottle will be altered. Why? When we suck the air out of it, the air present out side the bottle will exert pressure on the bottle in all possible directions. Therefore the bottle is crushed. This shows that air have pressure.

Another thing ,

to overcome such huge pressure we have blood pressure in our body and when we go to outer space there the space persons have nose bleeding because there is no pressure and hence some of our blood vessels explode out

Hope it would be helpful !