Explanation:

Ideal solution is defined as a mixture in which the enthalpy of mixing is zero. In other words, the solution behaves like a single component with respect to enthalpy. The ideal solution obeys Raoult's law and Henry's law.

Raoult's law states that the partial pressure of each component in the vapor phase of an ideal solution is directly proportional to its mole fraction in the liquid phase at a given temperature.

Henry's law states that the partial pressure of a gas in a liquid is directly proportional to the mole fraction of the gas in the liquid phase at a constant temperature.

Let's discuss each option given in the question and see which one is not an ideal solution.

a) C6H6 and C6H5 CH3:
Both benzene and toluene have similar intermolecular forces and molecular size, hence they form an ideal solution.

b) C2H6 and C2H5I:
Both ethane and ethyl iodide have similar intermolecular forces and molecular size, hence they form an ideal solution.

c) C6H5Cl and C6H5Br:
Both chlorobenzene and bromobenzene have similar intermolecular forces and molecular size, hence they form an ideal solution.

d) C2H5I and C2H5OH:
Ethyl iodide and ethanol have different intermolecular forces and molecular size. Ethyl iodide is non-polar, while ethanol is polar. Hence, they do not form an ideal solution.

Conclusion:
Therefore, the correct option is D, i.e., C2H5I and C2H5OH do not form an ideal solution.