Maximum -I effect is exerted by the group-

Options

A. `-C_(6)H_(5)`
B. `-OCH_(3)`
C. `-Cl`
D. `-NO_(2)`

Answer

To determine which group exerts the maximum -I (negative inductive) effect, we need to analyze the groups provided in the question. The -I effect refers to the electron-withdrawing ability of a substituent due to its electronegativity and its ability to stabilize negative charges.

### Step-by-Step Solution:

1. **Identify the Groups**: The groups mentioned in the question are:
- C6H5 (Benzene)
- OCH3 (Methoxy group)
- Halogens (e.g., Cl, Br, I)
- NO2 (Nitro group)

2. **Analyze C6H5 (Benzene)**:
- Benzene is a stable aromatic compound with delocalized electrons.
- It has a weak -I effect because it does not strongly withdraw electrons; instead, it can donate electrons through resonance.
- **Conclusion**: C6H5 has a minimal -I effect.

3. **Analyze OCH3 (Methoxy group)**:
- The oxygen in the methoxy group is electronegative and can withdraw electrons through its -I effect.
- However, it also has a +R (resonance) effect, which can counterbalance its -I effect.
- **Conclusion**: OCH3 has a moderate -I effect.

4. **Analyze Halogens**:
- Halogens (like Cl, Br, I) are electronegative and exhibit a -I effect.
- They withdraw electrons from the carbon chain but are less effective than stronger electron-withdrawing groups.
- **Conclusion**: Halogens have a moderate -I effect, stronger than benzene but weaker than nitro.

5. **Analyze NO2 (Nitro group)**:
- The nitro group is a strong electron-withdrawing group due to the presence of both electronegative oxygen atoms.
- It exerts a strong -I effect because it pulls electrons away from the carbon chain significantly.
- **Conclusion**: NO2 has the maximum -I effect among the groups listed.

6. **Rank the Groups**:
- Based on the analysis:
1. NO2 (Maximum -I effect)
2. OCH3 (Moderate -I effect)
3. Halogens (Moderate -I effect)
4. C6H5 (Minimal -I effect)

### Final Answer:
The group that exerts the maximum -I effect is **NO2**.