How to calculate the number of moles in a sample...?

A student collected a natural gas from a lab gas jet at 25 degrees Celsius (298 degrees Kelvin) in a 250 mL flask until the pressure of the gas was 550 torr (0.72368 atmospheres). I need to figure out the number of moles of the sample, the molecular m of the gas, and finally the name of that sample gas. Any help appreciated!