What is the value of ln y (where y = activity co-efficient) for ideal gases?

Solution (By Examveda Team)

Since activity co-efficient is defined as
$$\eqalign{ & {\gamma _i} = \frac{{{\text{Fugacity in real solution}}}}{{{\text{Fugacity in ideal solution}}}}, \cr & ln{\gamma _1} = \frac{{\overline {n{G^E}_l} }}{{RT}} = 0\left( {{\text{for ideal solution}}} \right), \cr} $$
Since there will be no excess gibbs free energy for ideal solution.
So, in the question it will be better if replace ideal gas by ideal solution.