The + l-effect is shown by

Options

A. `CH_3`
B. `-OH`
C. `F`
D. `-C_6 H_5`

Explanation

To determine which groups exhibit the +I (positive inductive) effect, we need to understand the concept of inductive effects in organic chemistry. The inductive effect is the permanent effect of the polarization of the electron density along a chain of atoms in a molecule due to the electronegativity differences between atoms.

### Step-by-Step Solution:

1. **Understanding Inductive Effect**:
- The inductive effect can be classified into two types: +I effect (electron-donating) and -I effect (electron-withdrawing).
- The +I effect occurs when a group has lower electronegativity than the carbon atom it is attached to, resulting in the donation of electron density towards the carbon chain.

2. **Identifying Groups**:
- Consider the groups provided in the question:
- CH3 (methyl group)
- OH (hydroxyl group)
- F (fluorine)
- Phenyl group (C6H5)

3. **Analyzing Each Group**:
- **CH3 (Methyl Group)**:
- Carbon in CH3 has the same electronegativity as the carbon in the chain. Therefore, it donates electron density to the carbon chain, exhibiting a +I effect.
- **OH (Hydroxyl Group)**:
- Oxygen is more electronegative than carbon, which means it pulls electron density away from the carbon chain. Thus, it exhibits a -I effect.
- **F (Fluorine)**:
- Fluorine is highly electronegative compared to carbon, so it also withdraws electron density from the carbon chain, showing a -I effect.
- **Phenyl Group (C6H5)**:
- The sp2 hybridized carbon in the phenyl group is more electronegative than the sp3 hybridized carbon in the chain, resulting in a -I effect as it withdraws electron density.

4. **Conclusion**:
- Among the groups analyzed, only the CH3 (methyl group) exhibits the +I effect. Therefore, the correct answer to the question is CH3.

### Final Answer:
The +I effect is shown by the CH3 (methyl) group.