The correct option is Benzene and toluene.
Explanation
An ideal solution is defined as a solution that obeys Raoult's Law over the entire range of concentration. For a solution to be ideal, the intermolecular attractive forces between the solute and solvent (A-B interactions) must be nearly identical in magnitude to those between the solute particles (A-A) and the solvent particles (B-B). This typically occurs when the components have similar chemical structures and polarity.
Analysis of Options:
- Benzene and toluene Benzene and Toluene: Both compounds are non-polar aromatic hydrocarbons with similar molecular structures and sizes. The intermolecular forces (London dispersion forces) existing in pure benzene and pure toluene are comparable to those in a mixture of the two. Consequently, there is no significant change in enthalpy or volume upon mixing, resulting in a nearly ideal solution.
- Ethanol and water Ethanol and Water: This mixture exhibits a positive deviation from Raoult's Law. The mixing of ethanol and water disrupts the strong hydrogen bonding network present in pure water, making the solution non-ideal.
- Phenol and aniline Phenol and Aniline: This mixture exhibits a negative deviation from Raoult's Law. Phenol (acidic) and aniline (basic) form strong intermolecular hydrogen bonds between the phenolic hydrogen and the nitrogen of aniline. These A-B interactions are stronger than the individual A-A or B-B interactions.
- Bromoethane and water Bromoethane and Water: These components have vastly different polarities and are not completely miscible. They do not form a homogeneous ideal solution; rather, they tend to show immiscibility or significant non-ideal behavior due to the hydrophobic nature of the alkyl halide against the hydrogen-bonded water structure.
Key Takeaway:
Ideal solutions are generally formed by liquid pairs that belong to the same homologous series or have very similar structures and polarity, such as benzene and toluene, or n-hexane and n-heptane.