Which of the following statement is true ?

Options

A. Trimethyl amines form a soluble compound with Hinsberg
reagent and KOH.
B. Dimethylamines react with KOH and phenol to form an azo dye.
C. Methyl amine reacts with nitrous acid and liberates `N_(2)`
D. none of these

Explanation

To solve the question regarding which statement is true, let's analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement**: "Trimethylamines form a soluble compound with Hinsburg reagent and alcoholic KOH."

- **Explanation**: The Hinsburg reagent (C6H5SO2Cl) is used to test for amines. Trimethylamine (N(CH3)3) does not react with the Hinsburg reagent to form a soluble compound. Therefore, this statement is **incorrect**.

### Step 2: Analyze the second statement
**Statement**: "Dimethylamines react with KOH and phenol to form an azo dye."

- **Explanation**: Azo dyes are typically formed from diazonium salts, which are derived from aromatic amines, not dimethylamines. The reaction mentioned does not lead to the formation of azo dyes. Therefore, this statement is also **incorrect**.

### Step 3: Analyze the third statement
**Statement**: "Methyl amine reacts with nitrous acid and liberates N2."

- **Explanation**: When methyl amine (CH3NH2) reacts with nitrous acid (HONO), it produces methanol (CH3OH), nitrogen gas (N2), and water (H2O). This reaction is characteristic of primary aliphatic amines, where nitrogen gas is liberated. Therefore, this statement is **correct**.

### Conclusion
After analyzing all three statements, we find that the **third statement** is true.

### Final Answer
The correct answer is: **Methyl amine reacts with nitrous acid and liberates N2.**

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