According to V.B.T., atoms of element form bond only to pair up their unpaired electrons present in ground state or excited state. This pairing of unpaired electron will take place by overlapping of orbitals each one having one unpaired electron with opposite spin.
Which of the following orbital combination does not form `pi`-bond ?

Options

A. `p_(x)+p_(x)` sideways overlapping
B. `d_(x^(2)-y^(2))+p_(y)` sideways overlapping
C. `d_(xy)+d_(xy)` sideways overlapping
D. `d_(yz)+p_(y)` sideways overlapping

Answer

To determine which orbital combination does not form a pi bond, we need to analyze the given options based on the principles of Valence Bond Theory (VBT). According to VBT, a sigma bond is formed by head-on (or axial) overlapping of orbitals, while a pi bond is formed by sideways overlapping of orbitals.

### Step-by-Step Solution:

1. **Understand the Types of Bonds**:
- **Sigma Bond (σ)**: Formed by the head-on overlap of orbitals.
- **Pi Bond (π)**: Formed by the sideways overlap of orbitals.

2. **Analyze Each Option**:
- **Option A: px + px**:
- The px orbitals overlap along the x-axis. This is a head-on overlap, which results in the formation of a sigma bond, not a pi bond.
- **Conclusion**: This combination does not form a pi bond.

- **Option B: dx² - y² + py**:
- The dx² - y² orbital overlaps with the py orbital. The dx² - y² is oriented along the x and y axes, while py is along the y-axis. This overlap is head-on, resulting in a sigma bond.
- **Conclusion**: This combination does not form a pi bond.

- **Option C: dx y + dx y**:
- The dx y orbitals overlap in a sideways manner, resulting in a pi bond due to the nature of their orientation.
- **Conclusion**: This combination forms a pi bond.

- **Option D: dyz + py**:
- The dyz orbital overlaps with the py orbital. The dyz orbital is oriented between the y and z axes, while py is along the y-axis. This overlap is sideways, resulting in a pi bond.
- **Conclusion**: This combination forms a pi bond.

3. **Final Conclusion**:
- The combinations that do not form a pi bond are **Option A (px + px)** and **Option B (dx² - y² + py)**. However, since the question asks for the option that does not form a pi bond, the correct answer is **Option B**.