Which of the following represent most effective `pi`-bond

Options

A. `2ppi-3ppi`
B. `3dpi-3dpi`
C. `2ppi-3dpi`
D. `3dpi-3ppi`

Answer

To determine which of the given options represents the most effective pi bond, we need to analyze the overlap of the orbitals involved in forming the pi bond. The effectiveness of a pi bond is influenced by the orientation and the size of the orbitals involved in the overlap.

### Step-by-Step Solution:

1. **Understanding Pi Bonds**:
- A pi bond is formed by the sideways overlap of p orbitals (or d orbitals in some cases). The effectiveness of a pi bond is maximized when the orbitals involved are aligned properly.

2. **Evaluating the Options**:
- **Option A: 2p and 3p**:
- The 2p orbital is smaller than the 3p orbital. This size difference can lead to poor overlap, making this pi bond less effective.

- **Option B: 3d and 3d**:
- Both orbitals are of the same type (3d) and have similar orientations. This allows for effective overlap, making this pi bond potentially very strong.

- **Option C: 2p and 3d**:
- The 2p orbital is much smaller and less diffuse compared to the 3d orbital. The mismatch in size and orientation leads to poor overlap, making this pi bond ineffective.

- **Option D: 3d and 3p**:
- The 3d orbital is more diffuse compared to the 3p orbital. The difference in size and orientation also results in ineffective overlap, thus a weaker pi bond.

3. **Conclusion**:
- Among the options, **Option B (3d and 3d)** provides the best overlap due to the similar size and orientation of the orbitals, making it the most effective pi bond.

### Final Answer:
**Option B (3d and 3d)** represents the most effective pi bond.

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