A sample containing 4.80 g of O2 gas has a volume of 15.0 L. Pressure and temperature remain constant. a) what is the new volume if 0.500 mol of O2 gas is added? b) Oxygen is released until the volume is 10.0 L. How many moles of O2 are removed? c) What is the volume after 4.00 g of He is added to the 4.80 g of O2 gas in the container