Which of the following amines forms a yellow oil with `NaNO_2//conc.HCl` ?

Options

A. `C_6H_5-NH-CH_3`
B. `C_6H_5-NH-C_6H_5`
C. `C_2H_5-NH-C_2H_5`
D. All of these

Answer

To solve the question of which amines form a yellow oil with `NaNO2` and `conc.HCl`, we need to understand the reaction that occurs between amines and nitrous acid (which is generated from `NaNO2` and `conc.HCl`).

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- When a secondary amine reacts with nitrous acid (HNO2), it forms a nitroso compound. This nitroso compound is typically a yellow oil.

2. **Identifying the Type of Amines**:
- We need to identify which of the given amines are secondary amines because primary amines will form different products (like diazonium salts) and tertiary amines do not react with nitrous acid in the same way.

3. **Analyzing the Options**:
- Check each option provided in the question to determine if they are secondary amines. A secondary amine has the structure R2NH, where R represents carbon chains or groups.

4. **Performing the Reaction**:
- For each secondary amine, write the reaction with nitrous acid:
- For example, if we have a secondary amine like `C2H5-NH-C2H5`, upon reaction with nitrous acid, it will yield a nitroso compound, which is a yellow oil.

5. **Conclusion**:
- After analyzing all the options, we find that the secondary amine(s) present will yield the yellow oil upon reaction with `NaNO2` and `conc.HCl`.

6. **Final Answer**:
- The correct option is the one that corresponds to the secondary amine.