6. While cleaning out a laboratory, a chemist found an unlabeled gas cylinder containing 7.5 x 10 mL of gas at 20.5°C at 1.50 atm of pressure. The chemist believed the mystery gas could be pure He, Ne, Ar, or Kr. Towards this end, the gas was found to have a mass of 1.88 g. What is the molar mass? What is the most likely identity of the mystery gas? 7. Assuming all gas is removed from the tank when filling balloons, how many 0.75 L balloons can be filled from a tank that containing 375 g CO, at 1.0 atm of pressure at a temperature of 298 K?