The species having + I effect are

Options

A. `-CH_3 CH_2`
B. `- COOH`
C. `- NO_2`
D. `(CH_3)_3 C-`

Answer

To determine the species that exhibit a +I effect, we need to understand what the +I effect is and identify the groups that can donate electron density to a carbon chain.

### Step-by-Step Solution:

1. **Understanding the +I Effect**:
- The +I effect (positive inductive effect) refers to the electron-donating ability of certain groups or atoms attached to a carbon chain. These groups increase the electron density on the carbon chain.

2. **Identifying Electron Donating Groups**:
- Alkyl groups (like methyl, ethyl, etc.) are known to have a +I effect because they can donate electron density to the carbon chain due to their lower electronegativity compared to carbon.

3. **Analyzing the Given Options**:
- Let's assume we have four options: A, B, C, and D. We need to analyze each option to see if they contain alkyl groups or other electron-donating groups.

4. **Evaluating Each Option**:
- **Option A**: If this contains an alkyl group, it will exhibit a +I effect.
- **Option B**: If this contains a group like -NO2 or -COOH, it will exhibit a -I effect (electron-withdrawing).
- **Option C**: Similar to B, if it contains an electron-withdrawing group, it will not exhibit a +I effect.
- **Option D**: If this also contains an alkyl group, it will exhibit a +I effect.

5. **Conclusion**:
- Based on the analysis, the species that exhibit a +I effect are those that contain alkyl groups. Therefore, the correct answers are **Option A and Option D**.

### Final Answer:
The species having a +I effect are **Option A and Option D**.