From Dalton's law of particle pressure pA=χAptotal and pB=χBptotal ptotal =pA+pB =4.5+5.5bar=10bar Substituting the values in above formula, 4.5=χA×10 χA=0.45 5.5=χB×10 χB=0.55 So, the mole fraction of A and B are 0.45 and 0.55 respectively.