In the mixture of phenol and aniline, the intermolecular hydrogen bonding between phenolic proton and lone pair on N-atom of aniline is stronger than the respective
intermolecular hydrogen bonding between two same molecules.
Thus, their mixture shows negative deviation from Raoult's law.
For such mixtures, ΔHmix <0 and ΔVmix <0
It forms a maximum boiling azeotrope.