Any help is appreciated!

2. Below is a plot of the natural log of the activity coefficients (lni) for a binary mixture of species a and b vs. the mole fraction of species a(xa) at 300K. a. What is the reference state for each species (Lewis-Randall or Henry's)? b. Show that the Gibbs-Duhem equation is satisfied at a mole fraction xa=0.6. c. Come up with an appropriate model for gmE for this system and find the values of the model parameter(s). d. Is it possible for species a and b to separate into two liquid phases? Explain