Which of the following combination of orbitals do / does not form bond (if x-axis is internuclear axis) ?

Options

A. `s+p_(z)`
B. `s+s`
C. `p_(z)+p_(x)`
D. `d_(xy)+p_(y)`

Explanation

To determine which combinations of orbitals do not form bonds when the x-axis is considered the internuclear axis, we will analyze each combination step by step.

### Step-by-Step Solution:

1. **Understanding the Internuclear Axis**:
- The x-axis is defined as the internuclear axis. This means that any orbital combination that approaches this axis will be analyzed for bonding potential.

2. **Combination A: s + pz**:
- The s orbital is spherical and has electron density uniformly distributed in all directions.
- The pz orbital has a specific orientation along the z-axis.
- When these two orbitals approach each other, the spherical s orbital can overlap with the pz orbital. However, since the pz orbital is not aligned along the x-axis, the effective overlap is minimal.
- **Conclusion**: This combination does not form a bond.

3. **Combination B: s + s**:
- Both orbitals are s orbitals, which are spherical.
- When two s orbitals approach each other, they can overlap effectively regardless of their orientation.
- **Conclusion**: This combination can form a sigma bond.

4. **Combination C: px + pz**:
- The px orbital is oriented along the x-axis, while the pz orbital is oriented along the z-axis.
- Since these orbitals are perpendicular to each other, there is no effective overlap between them.
- **Conclusion**: This combination does not form a bond.

5. **Combination D: dxy + py**:
- The dxy orbital has a specific orientation in the xy-plane, while the py orbital is oriented along the y-axis.
- These orbitals can overlap effectively because they are not perpendicular to each other.
- **Conclusion**: This combination can form a pi bond.

### Final Answer:
The combinations that do not form a bond are **A (s + pz)** and **C (px + pz)**.