A gas mixture with 4 mol of Ar, x moles of Ne, and y moles of Xe is prepared at a pressure of 1 bar and a temperature of 298 K. The total number of moles in the mixture is three times that of Ar. Write an expression for ?Gmixing in terms of x. At what value of x does ?Gmixing have its minimum value? Calculate ?Gmixing for this value of x.