When 1 mole of argon gas is bubbled through a large volume of an Fe-Mn melt of XMn=0.5 at 1850 K evaporation of Mn into the Ar causes the mass of the melt to decrease by 0.75 g. The gas leaves the melt at a pressure of 1 atm. Calculate the activity coefficient of Mn in the liquid alloy. Molar mass of Mn is 54.938 g/mol. The saturated vapor pressure of liquid Mn is given by