Calculate the molecular weight of freon-12, if 122.70 liters of its vapor at 200.00

PV = nRT

Where:

P = pressure in atm = 700/760 = 0.9211atm

V = volume = 8.29L

R = gas constant, 0.08206 atm-L/mol-K

T = temperature in Kelvin = 200 + 273 = 473

n = numbers of moles  = Mass/molar mass

mass of the compound = 30.5

we can rewrite the equation above as

PV = (Mass)/(Molar mass) * RT

let that person have a turn to speak : )

it is b that is the answer.