Among the following, that does not form an ideal solution is:

Options

A. `C_(6)H_(6) and C_(6)H_(5)CH_(3)`
B. `C_(2)H_(5)Cl and C_(2)H_(5)OH`
C. `C_(6)H_(5)Cl and C_(6)H_(5)Br`
D. `C_(2)H_(5)Br and C_(2)H_(5)I`

Answer

To determine which of the given pairs does not form an ideal solution, we need to analyze the interactions between the components of each pair based on their molecular structures and the principles of Raoult's law.

### Step-by-Step Solution:

1. **Understanding Ideal Solutions**:
- An ideal solution is one that obeys Raoult's law, which states that the vapor pressure of a solvent in a solution is directly proportional to the mole fraction of the solvent. Ideal solutions typically have similar molecular structures and interactions.

2. **Analyzing the Options**:
- **Option 1: Benzene (C6H6) and Toluene (C6H5CH3)**:
- Both benzene and toluene have similar molecular structures (both are aromatic hydrocarbons). The interactions (benzene-benzene, toluene-toluene, and benzene-toluene) are comparable, suggesting that this pair forms an ideal solution.

- **Option 2: Chloroethane (C2H5Cl) and Ethanol (C2H5OH)**:
- Chloroethane is a haloalkane, while ethanol is an alcohol. These two have different functional groups, leading to dissimilar intermolecular interactions (dipole-dipole interactions in ethanol vs. van der Waals forces in chloroethane). This difference indicates that they do not form an ideal solution.

- **Option 3: Chloroethane (C2H5Cl) and Bromoethane (C2H5Br)**:
- Both are haloalkanes and share similar molecular structures. The interactions among them (chloro-chloro, bromo-bromo, and chloro-bromo) are similar, indicating that they form an ideal solution.

- **Option 4: Bromoethane (C2H5Br) and Iodoethane (C2H5I)**:
- Similar to chloroethane and bromoethane, both bromoethane and iodoethane are haloalkanes with comparable structures. Their interactions are also similar, suggesting they form an ideal solution.

3. **Conclusion**:
- Based on the analysis, the pair that does not form an ideal solution is **Option 2: Chloroethane and Ethanol**.

### Final Answer:
**Option 2: Chloroethane and Ethanol does not form an ideal solution.**