Which of the following on reactions with nitrous acid, followed by treatment with `NaOH` produces a blue coluration?

Options

A. `RCH_(2)NO_(2)`
B. `R_(3)CNO_(2)`
C. `R_(2)CHNO_(2)`
D. `PhCNO_(2)`

Answer

To solve the question regarding which compound produces a blue coloration upon reaction with nitrous acid followed by treatment with sodium hydroxide, we can analyze each option step by step.

### Step 1: Identify the nature of the compounds
We have four options, and we need to identify whether they are primary, secondary, or tertiary amines, as this will affect their reactivity with nitrous acid.

1. **Option 1: RCH2NH2 (Primary amine)**
2. **Option 2: R3CNO2 (Tertiary nitro compound)**
3. **Option 3: R2CHNO2 (Secondary amine)**
4. **Option 4: pH, CH2, and NO2 (Primary nitro compound)**

### Step 2: Reaction with Nitrous Acid (HNO2)
- **Primary Amines**: React with nitrous acid to form nitroso compounds, which can further react to form nitrolic acids.
- **Tertiary Amines**: Do not react with nitrous acid due to the absence of alpha hydrogen.
- **Secondary Amines**: React with nitrous acid to form nitroso compounds, which can lead to the formation of pseudonitriles.

### Step 3: Analyze each option
1. **Option 1 (RCH2NH2)**:
- Reacts with HNO2 to form nitroso compound and then nitrolic acid. This does not produce a blue color but a blood-red color.

2. **Option 2 (R3CNO2)**:
- Tertiary nitro compound does not react with nitrous acid due to the lack of alpha hydrogen. Thus, it does not produce any color.

3. **Option 3 (R2CHNO2)**:
- This is a secondary amine that reacts with nitrous acid to form a nitroso compound, which can further lead to the formation of pseudonitriles. Pseudonitriles are known to produce a blue coloration.

4. **Option 4 (pH, CH2, and NO2)**:
- This is another primary nitro compound that will not produce a blue color upon reaction with nitrous acid.

### Conclusion
From the analysis, **Option 3 (R2CHNO2)** is the correct answer as it produces a blue coloration upon reaction with nitrous acid followed by treatment with sodium hydroxide.