A perfectly ideal solution is rare but some solution behave nearly ideal. Which of the following does not fall in this category?

Ethanol and acetone

The correct answer is Option (2) → Ethanol and acetone

Nearly ideal solutions are formed when:

• Intermolecular forces between unlike molecules ≈ like molecules

• No hydrogen bonding or strong interactions

• Similar molecular size and nature

Option 1: n-hexane and n-heptane - Both are non-polar hydrocarbons. Similar structure and intermolecular forces. Behave nearly ideal.

Option 2: Ethanol and acetone Ethanol forms hydrogen bonding. Acetone can interact strongly with ethanol through hydrogen bonding. Unlike interactions differ significantly from pure liquids. Hence non-ideal solution.

Option 3: Benzene and toluene - Both are non-polar aromatic compounds. Similar molecular size and forces. Behave nearly ideal.

Option 4: Bromoethane and chloroethane - Similar polar molecules with comparable structure. Intermolecular forces are similar. Behave nearly ideal.