The label has come off a cylinder of gas in your laboratory. You know only that one species of gas is contained in the cylinder, but you do not know whether it is hydrogen, oxygen, helium, nitrogen,...

Extracted text: The label has come off a cylinder of gas in your laboratory. You know only that one species of gas is contained in the cylinder, but you do not know whether it is hydrogen, oxygen, helium, nitrogen, acetylene, or argon. To find out, you evacuate a 3.00-liter flask, seal it and weigh it, and then let gas from the cylinder flow into it until the gauge pressure equals 1.00 atm. The flask is reweighed, and the mass of the added gas is found to be 7.8474 g. Room temperature is 25.0°C, and barometric pressure is 1.00 atm. What is the gas?