Step 1: Recall Raoult's law and deviations.
Raoult's law holds for an ideal solution where the forces between unlike molecules (A-B) are the same as those between like molecules (A-A and B-B). A deviation appears when these forces differ.
Step 2: Decide the kind of deviation.
If the new A-B forces are stronger than the original forces, the molecules are held more tightly, fewer escape into vapour, the vapour pressure falls below the ideal value, and we get a negative deviation.
Step 3: Look at phenol and aniline.
Phenol has an \(-OH\) group and aniline has an \(-NH_2\) group. When mixed, they form strong intermolecular hydrogen bonds (O-H...N) between the two different molecules.
Step 4: Connect the cause to the result.
These new hydrogen bonds are stronger than the forces present in pure phenol and pure aniline. So the escaping tendency of molecules decreases and the vapour pressure becomes lower than expected.
Step 5: Conclude.
A mixture of phenol and aniline shows a negative deviation from Raoult's law, because of strong intermolecular hydrogen bonding between the unlike molecules.
Answer: The mixture shows negative deviation from Raoult's law, due to strong hydrogen bonding between phenol and aniline which lowers the vapour pressure below the ideal value.