Identify the mixture that shows positive deviations from Raoult's Law

We need to identify the mixture that shows positive deviation from Raoult's Law.

Key Concept: Positive deviation from Raoult's Law occurs when the interactions between unlike molecules (A-B) are weaker than the interactions between like molecules (A-A and B-B). This causes the vapor pressure of the solution to be higher than predicted by Raoult's Law, because molecules escape the solution more easily.

Option 1: Acetone + Aniline ($$(CH_3)_2CO + C_6H_5NH_2$$):

Acetone and aniline form hydrogen bonds with each other (C=O of acetone with N-H of aniline). A-B interactions are stronger than average A-A and B-B interactions. This gives negative deviation.

Option 2: Chloroform + Benzene ($$CHCl_3 + C_6H_6$$):

Chloroform and benzene have weak attractive interactions (dipole-induced dipole). These are comparable to the original interactions, giving nearly ideal behavior or slight negative deviation.

Option 3: Chloroform + Acetone ($$CHCl_3 + (CH_3)_2CO$$):

Chloroform forms hydrogen bonds with acetone (C-H...O=C). The A-B interactions are stronger, giving negative deviation.

Option 4: Acetone + Carbon disulfide ($$(CH_3)_2CO + CS_2$$):

Acetone has dipole-dipole interactions (polar molecule), while $$CS_2$$ is non-polar. When mixed, the strong dipole-dipole interactions of acetone are disrupted, and the new A-B interactions (dipole-induced dipole) are weaker. This makes it easier for molecules to escape into the vapor phase, resulting in positive deviation.

The correct answer is Option (4): $$(CH_3)_2CO + CS_2$$.