+ I effect is shown by

Options

A. `- CH_3`
B. - Br
C. - Cl
D. `- NO_2`

Answer

To solve the question regarding which groups exhibit the +I effect, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Inductive Effect**:
The inductive effect refers to the permanent polarization of a bond due to the electronegativity difference between atoms. It can be classified into two types: +I effect (electron-donating) and -I effect (electron-withdrawing).

2. **Define +I Effect**:
The +I effect is exhibited by groups that donate electron density to the rest of the molecule. This effect increases the electron density on adjacent atoms.

3. **Identify Electron-Donating Groups**:
Common examples of groups that show the +I effect are alkyl groups (e.g., CH3, C2H5). These groups are less electronegative and can push electron density towards the rest of the molecule.

4. **Evaluate the Given Options**:
- **Option 1: CH3 (Methyl group)**: This is an alkyl group and exhibits the +I effect.
- **Option 2: Bromine (Br)**: This is a halogen and exhibits the -I effect (electron-withdrawing).
- **Option 3: Chlorine (Cl)**: Similar to bromine, chlorine is also a halogen and exhibits the -I effect.
- **Option 4: Nitro group (NO2)**: This is a strong electron-withdrawing group and exhibits the -I effect.

5. **Conclusion**:
Among the options provided, only the CH3 group shows the +I effect. Therefore, the correct answer is **Option 1: CH3**.