A mixture of and has a volume of 130.0 cm^3 at 0.00 degrees C and 1 atm . The mixture is cooled to the temperature of liquid nitrogen at which ammonia freezes out and the remaining gas is removed from the vessel. Upon warming the vessel to 0.00 degrees C and 1 atm , the volume is 74.0 cm^3 .Calculate the mole fraction of in the original mixture.