Question

Which of the following form an ideal solution?
(I) Chloroethane and bromoethane (II) Benzene and toluene \[ \text{(III) } n\text{-Hexane and } n\text{-heptane} \] (IV) Phenol and aniline

• A. I & II only
• B. I, II & III only
• C. II, III & IV only
• D. I & IV only

Hint:

Ideal solutions are generally formed by chemically similar liquids having nearly equal intermolecular forces, such as benzene-toluene or hexane-heptane.

Answer 1

The Correct Option is B

Step 1: Understand ideal solution.
An ideal solution is one which obeys Raoult's law over the entire range of concentration.
For an ideal solution: \[ \Delta H_{\text{mix}}=0 \] and \[ \Delta V_{\text{mix}}=0 \] This happens when interactions between unlike molecules are almost equal to interactions between like molecules.

Step 2: Check pair (I).
Chloroethane and bromoethane are chemically similar haloalkanes.
Their intermolecular forces are nearly similar.
Hence, they form an ideal solution.

Step 3: Check pair (II).
Benzene and toluene are non-polar aromatic compounds.
Their molecular structures and intermolecular forces are similar.
Hence, they form an ideal solution.

Step 4: Check pair (III).
\(n\)-Hexane and \(n\)-heptane are homologous hydrocarbons.
They have similar molecular nature and similar van der Waals interactions.
Hence, they form an ideal solution.

Step 5: Check pair (IV).
Phenol and aniline do not form an ideal solution because they show strong specific interactions such as hydrogen bonding.
Due to these interactions, \[ \Delta H_{\text{mix}}\neq0 \] and the solution deviates from ideal behavior.

Step 6: Final conclusion.
Thus, the pairs forming ideal solutions are: I, II and III only Hence, the correct answer is \[ \boxed{\text{I, II \& III only}} \]