For an ideal liquid solution, which of the following is unity?

Answer: Option 3

For an ideal liquid solution the activity coefficient will be equal to 1. Since, activity coefficient of a species is defined as \[{{\gamma }_{i}}=\frac{\text{fugacity of the species in the real solution}\left( \widetilde{{{f}_{l}}} \right)}{\text{fugacity of the species in the ideal solution}\left( \widetilde{{{f}_{l}}^{ld}} \right)}\] For ideal solution \[\widetilde{{{f}_{l}}}=\widetilde{{{f}_{l}}^{ld}}\] \[{\rm{So, }}{\gamma _i} = 1\]