What is pressure inside lungs when you breath and the pressure outside is 2 atm?
idk...2 ATM because thats what surrounds you
Right - 2 atm. So it is the same pressure as the one outside. If the pressures are identical, there is no reason for breathing to be more difficult.
Is breathing using compreesed air in scuba diving harder, or not
i think that it would be harder because of the pressure in the water
It is not. Scuba pressure regulator is made in such a way, that it supplies you with the air of the same pressure than water around you has. That's why you can breath.
Imagine you have huge tank and inside of this tank there is 1L jar without lid. When the air in the tank is at 1 atm - what is volume of the air in the jar? Now we incerase pressure in the tank to 2 atm. What is volume of the air in jar now?
Back to your lungs - imagine yourself in the same place the jar was before
Is there any change in the volume of your lungs when the pressure rises?