A mixture of chloroform and acetone forms a solution with a negative deviation from Raoult's law. because chloroform molecule is able to form hydrogen bonds with acetone molecules.

Due to $H$-bonding type interactions formed between the hydrogen atom of chloroform and 'pi' electron cloud of the benzene ring. chloroform-benzene interactions are stronger than chloroform-chloroform and benzene-benzene interactions. thus show a negative deviation from Raoult's law.

Acetone – Benzene show positive deviation.