The primary, secondary and tertiary amines can be best distinguished by

Options

A. mustard oil reaction
B. carbylamine reaction
C. exhaustive alkylation
D. `HNO_(2)` treatment

Explanation

To distinguish between primary, secondary, and tertiary amines, we can utilize the treatment of these amines with nitrous acid (HNO2). Here’s a step-by-step solution:

### Step 1: Understanding the Reactions
- **Primary Amines (RNH2)**: When treated with nitrous acid (HNO2), primary amines react to form nitrogen gas (N2) and alcohol. This reaction is characterized by the evolution of gas.

- **Secondary Amines (R2NH)**: When secondary amines are treated with nitrous acid, they produce an insoluble oil (N-nitroso derivative) instead of nitrogen gas.

- **Tertiary Amines (R3N)**: Tertiary amines do not react with nitrous acid in the same way. They typically yield a clear solution without the formation of gas or oil.

### Step 2: Conducting the Experiment
1. **Prepare the Samples**: Take three different amines: one primary (e.g., ethylamine), one secondary (e.g., diethylamine), and one tertiary (e.g., triethylamine).

2. **Add Nitrous Acid**: Treat each amine with a cold acidic solution of nitrous acid.

### Step 3: Observing the Results
- **For Primary Amine**: Observe the evolution of nitrogen gas (bubbles).
- **For Secondary Amine**: Look for the formation of an insoluble oil.
- **For Tertiary Amine**: Note that no gas or oil is formed; the solution remains clear.

### Step 4: Conclusion
Based on the observations:
- The primary amine is confirmed by the release of nitrogen gas.
- The secondary amine is identified by the formation of an insoluble oil.
- The tertiary amine is recognized by the absence of any reaction (clear solution).

Thus, the best method to distinguish between primary, secondary, and tertiary amines is through their reaction with nitrous acid (HNO2).

### Final Answer
**D. HNO2 treatment is the best method to distinguish between primary, secondary, and tertiary amines.**

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