Which of the following is not a chromophore?

Options

A. `-N=N-`
B. `-NO`
C. `-NO_2`
D. `-NH_2`

Answer

To determine which of the following options is not a chromophore, we first need to understand the definitions of chromophores and auxochromes.

### Step-by-Step Solution:

1. **Definition of Chromophore**: A chromophore is a part of a molecule responsible for its color. It typically contains unsaturated groups (like double or triple bonds) that can absorb visible light.

2. **Definition of Auxochrome**: An auxochrome is a functional group that does not itself produce color but can modify the color of the chromophore by affecting its ability to absorb light. Common auxochromes include -OH (hydroxyl), -NH2 (amino), and -COOH (carboxyl).

3. **Analyzing the Options**:
- **Option 1**: Contains a double bond (unsaturated compound) → This is likely a chromophore.
- **Option 2 (NO)**: Contains a double bond between nitrogen and oxygen → This is a chromophore.
- **Option 3 (NO2)**: Contains double bonds and is unsaturated → This is also a chromophore.
- **Option 4 (NH2)**: This is an amino group, which is a basic functional group and does not have unsaturation → This is an auxochrome, not a chromophore.

4. **Conclusion**: Based on the definitions and analysis, the correct answer is that **NH2 is not a chromophore**; it is an auxochrome.

### Final Answer:
**Option 4: NH2 is not a chromophore.**