If y-axis is the approaching axis between two atoms, then which of the set of orbitals can not form the `pi` bond between two atoms in general

Options

A. `p_(z)-p_(z)`
B. `p_(x)-p_(x)`
C. `p_(x)-p_(y)`
D. none of these

Answer

To determine which set of orbitals cannot form a pi bond between two atoms when the y-axis is the approaching axis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Orbital Orientation**:
- The y-axis is the axis along which the two atoms are approaching each other.
- The relevant orbitals for forming bonds are the p orbitals: Px, Py, and Pz.

2. **Identifying Sigma and Pi Bonds**:
- A sigma (σ) bond is formed by the head-on overlap of orbitals, while a pi (π) bond is formed by the sideways overlap of orbitals.
- For example, when Py orbitals overlap along the y-axis, they will form a sigma bond because of the head-on overlap.

3. **Analyzing Overlap of Different Orbitals**:
- **Px and Px**: These orbitals can overlap sideways, resulting in a pi bond.
- **Py and Py**: These orbitals will overlap along the y-axis, resulting in a sigma bond.
- **Pz and Pz**: These orbitals can also overlap sideways, resulting in a pi bond.

4. **Examining the Combination of Px and Py**:
- When considering the overlap of Px and Py orbitals, we find that they are oriented perpendicular to each other.
- There is no common electron cloud between Px and Py orbitals when they approach each other along the y-axis.

5. **Conclusion**:
- Since Px and Py do not have overlapping electron clouds, they cannot form either a sigma or a pi bond.
- Therefore, the set of orbitals that cannot form a pi bond is **Px and Py**.

### Final Answer:
The set of orbitals that cannot form a pi bond between two atoms when the y-axis is the approaching axis is **Px and Py**.