how many molecules of air are there in 1 litre flask at 293K, if the preessure in it is 0.3 atm.

Answer 1

Use the ideal gas law:

P*V = n*R*T

Solve for n, the number of moles
R = 0.08206 l-atm/mole*K
T = 293

n = 0.01248 moles

Multiply that by Avogadro's number for the number of molecules.