Which of the following group shown `+mgt - I` effect?

Options

A. `-F`
B. `-O-overset(O)overset(||)C-R`
C. `-underset(O)underset(||)C-R`
D. `-COOH`

Answer

To determine which of the following groups shows a +M (mesomeric) effect greater than -I (inductive) effect, we need to analyze the groups based on their electronic properties.

### Step-by-Step Solution:

1. **Understanding the Effects**:
- **+M Effect (Mesomeric Effect)**: This effect is due to the delocalization of electrons through pi bonds or lone pairs adjacent to a pi system. It generally occurs when a group can donate electron density to a conjugated system.
- **-I Effect (Inductive Effect)**: This effect is the polarization of sigma bonds due to electronegative atoms or groups that attract electron density towards themselves, leading to a decrease in electron density on the adjacent atoms.

2. **Analyzing Each Group**:
- **Group A: -F (Fluorine)**: Fluorine is highly electronegative and will pull electron density towards itself, showing a -I effect. It does not have a +M effect because it cannot donate electron density effectively. Thus, this group does not satisfy our requirement.

- **Group B: O=C=O (Carbonyl Group)**: The carbonyl group has oxygen, which is electronegative and can withdraw electron density (-I effect). However, the lone pair on oxygen can also participate in resonance with the carbonyl carbon, leading to a +M effect. The +M effect here is stronger than the -I effect, making this group a candidate for our answer.

- **Group C: C=O (Carbonyl)**: Similar to Group B, the carbonyl oxygen is electronegative and will exhibit a -I effect. There is no significant +M effect since the lone pair on oxygen is not effectively participating in resonance. Thus, this group does not satisfy our requirement.

- **Group D: COOH (Carboxylic Acid)**: The carboxylic acid group has two electronegative oxygen atoms. The -I effect dominates here, as both oxygens will pull electron density towards themselves, and there is no significant +M effect. Therefore, this group does not satisfy our requirement.

3. **Conclusion**:
- After analyzing all the groups, only **Group B (O=C=O)** shows a +M effect that is greater than the -I effect. Thus, the correct answer is **Group B**.

### Final Answer:
The group that shows +M greater than -I effect is **O=C=O (Group B)**.