$(25$ pts$)$ Consider a binary mixture of species $(1)$ and $(2).$ The activity coefficients for this

mixture are described by the one constant Margules equation:

$G_{{?}^{?}}(Ex)=A{x}_1{x}_2$

Here, you are asked to consider the temperature and pressure dependence of the parameter $A.$

a$.$ If $H_{{?}_{?}}(mix)=0,$ what can you say about the Margules parameter $A?$

b$.$ If $V_{{?}_{?}}(mix)=0,$ what can you say about the Margules parameter $A?$