The compound which on reaction with cold nitrous acid gives oily nitrosoamine is

Options

A. methyl amine
B. ethyl amine
C. diethyl amine
D. triethyl anine

Explanation

To solve the question, we need to identify which compound, when reacted with cold nitrous acid, produces an oily nitrosoamine. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Understanding the Reactants**:
- We are dealing with nitrous acid (HNO2) and various types of amines (primary, secondary, and tertiary).
- Nitrous acid reacts differently with these amines, leading to different products.

2. **Types of Amines**:
- **Primary amines (1°)**: React with nitrous acid to form stable diazonium salts, which are not oily.
- **Secondary amines (2°)**: React with nitrous acid to form nitrosoamines, which can be oily.
- **Tertiary amines (3°)**: Do not react with nitrous acid.

3. **Identifying the Correct Amine**:
- The question specifies that we are looking for a compound that gives an oily nitrosoamine upon reaction with cold nitrous acid.
- Among the given options, we need to identify which one is a secondary amine.

4. **Analyzing the Options**:
- **Methylamine**: This is a primary amine.
- **Ethylamine**: This is also a primary amine.
- **Diethylamine**: This is a secondary amine (C2H5)2NH.
- **Triethylamine**: This is a tertiary amine.

5. **Reaction with Cold Nitrous Acid**:
- When diethylamine (a secondary amine) reacts with cold nitrous acid, it forms an oily nitrosoamine:
\[ \text{(C}_2\text{H}_5)_2\text{NH} + \text{HNO}_2 \rightarrow \text{(C}_2\text{H}_5)_2\text{N}=\text{O} + \text{H}_2\text{O} \]
- The product formed is (C2H5)2N=O, which is the oily nitrosoamine.

6. **Conclusion**:
- The compound that reacts with cold nitrous acid to give an oily nitrosoamine is **diethylamine**.

### Final Answer:
The compound which on reaction with cold nitrous acid gives oily nitrosoamine is **diethylamine**.