All form ideal solutions except

Options

A. `C_2H_5Br and C_2H_5I`
B. `C_6H_5Cl and C_6 H_5Br`
C. `C_6H_6 and C_6H_5 CH_3`
D. `C_2H_5I and C_2H_5 OH`

Answer

To solve the question "All form ideal solutions except," we need to analyze the provided options and determine which pairs of substances do not form ideal solutions based on their molecular structures and the principles of Raoult's law.

### Step-by-Step Solution:

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

2. **Identify the Options**:
- The options provided are:
1. C2H5-Br and C2H5-I
2. C6H5Cl and C6H5Br
3. C6H6 (Benzene) and C6H5-CH3 (Toluene)
4. Iodoethane and Ethanol

3. **Analyze Each Pair**:
- **Option 1: C2H5-Br and C2H5-I**:
- Both have a common ethyl (C2H5) group and differ only in the halogen (Br and I). They are similar in structure and can be considered an ideal solution.
- **Option 2: C6H5Cl and C6H5Br**:
- Both are derivatives of benzene (Chlorobenzene and Bromobenzene) and have similar structures. They can also be considered an ideal solution.
- **Option 3: C6H6 and C6H5-CH3**:
- Benzene and Toluene have similar skeletal structures (both are aromatic compounds). They form an ideal solution.
- **Option 4: Iodoethane and Ethanol**:
- Iodoethane (C2H5I) contains a halogen, while ethanol (C2H5OH) contains an alcohol group. The difference in functional groups leads to dissimilar interactions and structures, making this pair a non-ideal solution.

4. **Conclusion**:
- Based on the analysis, the pair that does not form an ideal solution is **Iodoethane and Ethanol**. Therefore, the answer to the question is option 4.

### Final Answer:
**Iodoethane and Ethanol do not form ideal solutions.**

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