Oxygen is present in a flask of 1.12L capacity at a pressure of 7.6×10−10 mm of Hg at 00C . The number of oxygen molecules in the flask is

PV=nRT                         PV=num of molecules6.023×1023RT 7.6×10−10760×1.12=num of molecules6.023×1023×22.4273×2 ∴ num of molecules=3.0115×1010