Intermolecular hydrogen bonding is observed between chloroform and ac…

The correct answer is Option (2) → (B) and (D) are correct

Raoult's law describes the vapor pressure of ideal solutions. A solution obeys Raoult's law when the intermolecular forces between unlike molecules (A–B) are approximately equal to those between like molecules (A–A and B–B).

However, deviations from Raoult's law occur when the intermolecular interactions change significantly upon mixing.

Intermolecular interaction in chloroform and acetone

Chloroform (CHCl₃) contains a hydrogen atom attached to carbon that becomes slightly positively polarized due to the presence of three electronegative chlorine atoms.

Acetone contains a carbonyl group (C=O) with a lone pair of electrons on oxygen.

Thus, a hydrogen bond forms between:

H of CHCl₃ → O of acetone

This intermolecular hydrogen bonding between unlike molecules is stronger than the interactions present in the pure liquids.

Effect on Raoult's law

When A–B interactions are stronger than A–A and B–B interactions:

• Molecules are held more strongly in the liquid phase
• Fewer molecules escape into the vapor phase
• Vapor pressure decreases

This results in a negative deviation from Raoult's law.

Option-wise Explanation

Option (A): Show positive deviation from Raoult's law

Positive deviation occurs when intermolecular forces between unlike molecules are weaker than those in the pure components. Since chloroform and acetone form hydrogen bonds (strong interaction), this option is incorrect.

Option (B): Show negative deviation from Raoult's law

Stronger intermolecular attraction between chloroform and acetone molecules leads to negative deviation from Raoult's law. Therefore this statement is correct.

Option (C): Obey Raoult's law

Ideal solutions obey Raoult's law when intermolecular forces remain unchanged. Because strong hydrogen bonding occurs here, the solution does not behave ideally. Hence this statement is incorrect.

Option (D): Show decrease in vapor pressure

Stronger intermolecular forces reduce the number of molecules escaping into the vapor phase, causing a decrease in vapor pressure. Therefore this statement is correct.