Which one of the following is a chromophoric group ?

Options

A. `-N=N-`
B. `-OH`
C. `-SO_3H`
D. `-NH_2`

Answer

To determine which of the given options is a chromophoric group, we need to understand the definition and characteristics of chromophores.

### Step-by-Step Solution:

1. **Understanding Chromophores**:
- A chromophore is a part of a molecule responsible for its color. It can absorb certain wavelengths of light, which leads to the appearance of color in compounds. The term "chromophore" comes from the Greek words "chroma" meaning color and "phore" meaning bearer.

2. **Identifying the Options**:
- We are given the following options:
- (a) N=N (double bond between two nitrogen atoms)
- (b) OH (hydroxyl group)
- (c) SO3H (sulfonic acid group)
- (d) NH2 (amino group)

3. **Analyzing Each Option**:
- **Option (a) N=N**: This is a double bond between two nitrogen atoms. This structure can absorb light and is known to impart color, making it a chromophore.
- **Option (b) OH**: This is a hydroxyl group, which is not a chromophore but an oxochrome, as it can enhance the color of a compound but does not itself impart color.
- **Option (c) SO3H**: This is a sulfonic acid group, which is also an oxochrome and does not act as a chromophore.
- **Option (d) NH2**: This is an amino group, which is another oxochrome and does not impart color by itself.

4. **Conclusion**:
- Among the given options, the only group that acts as a chromophore is **N=N (double bond between nitrogen atoms)**. Therefore, the correct answer is **(a) N=N**.

### Final Answer:
The chromophoric group among the options is **N=N**.