Explanation:

An ideal solution is a solution in which the interactions between the solute and solvent molecules are the same as the interactions between the solvent molecules themselves. In an ideal solution, the enthalpy of mixing is zero, and the solution behaves like an ideal gas.

Option A: Solution of benzene in toluene
Benzene and toluene are both aromatic hydrocarbons with similar chemical structures and intermolecular forces. They exhibit strong intermolecular interactions, such as van der Waals forces and π-π stacking. Therefore, a solution of benzene in toluene can be considered an ideal solution.

Option B: Solution of ethyl and propyl alcohol
Ethyl alcohol and propyl alcohol are both alcohols with similar chemical structures and intermolecular forces. They exhibit hydrogen bonding, which is a strong intermolecular force. Therefore, a solution of ethyl and propyl alcohol can be considered an ideal solution.

Option C: Paraffin hydrocarbon gas in paraffin oil
Paraffin hydrocarbon gas and paraffin oil are both hydrocarbons with similar chemical structures and intermolecular forces. They exhibit weak intermolecular forces, such as van der Waals forces. Therefore, a solution of paraffin hydrocarbon gas in paraffin oil can be considered an ideal solution.

Option D: Solution of isobutane and olefins
Isobutane and olefins are not similar in their chemical structures and intermolecular forces. Isobutane is a saturated hydrocarbon, while olefins are unsaturated hydrocarbons with double bonds. The presence of double bonds in olefins leads to stronger intermolecular forces compared to isobutane. Therefore, a solution of isobutane and olefins cannot be considered an ideal solution.

In summary,
Option D, the solution of isobutane and olefins, is not an example of an ideal solution because the solute (olefins) and solvent (isobutane) have different chemical structures and intermolecular forces. The interactions between the solute and solvent molecules are not the same as the interactions between the solvent molecules themselves, leading to non-zero enthalpy of mixing and deviation from ideal solution behavior.