Which among the following is very strong o-p-directing groups?

Options

A. `-Cl`
B. `-OR`
C. `-NH_(2)`
D. `-NHR`

Explanation

To determine which among the given options is a very strong ortho-para directing group in the context of benzene chemistry, we need to analyze the substituents based on their electronic effects—specifically, their ability to donate electron density to the benzene ring.

### Step-by-Step Solution:

1. **Understanding Directing Effects**:
- Ortho-para directing groups are those that increase the electron density on the benzene ring at the ortho and para positions relative to themselves. This is typically due to resonance effects where the substituent can donate electron density.

2. **Identifying the Groups**:
- The question lists several groups. We need to evaluate each one based on their ability to donate electrons to the benzene ring:
- **Cl (Chlorine)**: This group is a halogen and is typically a weak ortho-para director due to its electronegativity and inability to donate electron density effectively.
- **NH2 (Amino group)**: This group has a lone pair of electrons on nitrogen which can be donated to the benzene ring, making it a strong ortho-para director.
- **NHR (Amine group)**: Similar to NH2, this group also has a lone pair available for resonance donation, making it a strong ortho-para director as well.
- **OH (Hydroxyl group)**: This group can also donate electron density through resonance, acting as a strong ortho-para director.

3. **Evaluating the Strength of Directing Effects**:
- Among the groups mentioned, the amino group (NH2) is particularly strong due to its ability to significantly increase electron density on the benzene ring. The NHR group is also strong, but the NH2 group is generally considered stronger because it has no steric hindrance and can donate its lone pair more effectively.

4. **Conclusion**:
- The strongest ortho-para directing group among the options provided is **NH2 (Amino group)**.

### Final Answer:
**NH2 (Amino group) is a very strong ortho-para directing group.**