Which of the following has +R (resonance) effect?

Options

A. `-CN`
B. `-CHO`
C. `-NH_(2)`
D. `-NO_(2)`

Answer

To determine which of the given options has a +R (resonance) effect, we need to understand what the +R effect means. The +R effect, or resonance effect, occurs when a substituent group can donate electron density into a conjugated system, typically through resonance.

### Step-by-Step Solution:

1. **Understanding the +R Effect**:
- The +R effect is associated with electron-donating groups. These groups typically contain lone pairs of electrons that can be delocalized into the π system of the molecule.
- For a group to exhibit a +R effect, it must have at least one lone pair of electrons.

2. **Analyzing the Given Options**:
- We need to analyze each option provided in the question to see if they can donate electrons through resonance.

3. **Option A: Nitrogen with a Lone Pair**:
- If nitrogen is attached to a carbon atom and has a lone pair, it can donate this lone pair into the π system, thus showing a +R effect.

4. **Option B: Oxygen with a Lone Pair**:
- If oxygen is attached to a carbon atom, it also has lone pairs. However, oxygen is more electronegative than carbon, which can lead to a -R effect instead of a +R effect.

5. **Option C: Nitrogen Attached to Two Electronegative Atoms**:
- If nitrogen is bonded to two electronegative atoms (like oxygen), it will withdraw electron density due to the electronegativity of those atoms, thus exhibiting a -R effect.

6. **Option D: Carbon with No Lone Pairs**:
- If carbon is bonded to other atoms without any lone pairs, it cannot donate electrons and will not exhibit a +R effect.

7. **Conclusion**:
- The only option that shows a +R effect is the one where nitrogen has a lone pair that can be donated into the π system.

### Final Answer:
- The option that exhibits the +R (resonance) effect is the one with nitrogen containing a lone pair.