Which of the following orbitals will not form sigma bond after overlapping ?

Options

A. s - orbital and s- orbital
B. s- orbital and `p_(z) -` orbital
C. `p_(z)`- orbital and `p_(z)-` orbital
D. `p_(x)`-orbital and `p_(y)`- orbital

Answer

To determine which of the given orbitals will not form a sigma bond after overlapping, we need to analyze each option based on the nature of sigma bonds and the types of orbitals involved.

### Step-by-Step Solution:

1. **Understanding Sigma Bonds**:
- A sigma bond is formed by the head-on (axial) overlap of orbitals. This means that the orbitals must be oriented in such a way that they can directly overlap along the axis connecting the two nuclei.

2. **Analyzing Each Option**:
- **Option A: s orbital and s orbital**:
- Both s orbitals are spherical and can overlap directly. Therefore, they can form a sigma bond.

- **Option B: s orbital and pz orbital**:
- If the s orbital is aligned along the z-axis, it can overlap with the pz orbital (which also has a lobe along the z-axis). This overlap is head-on and will result in the formation of a sigma bond.

- **Option C: pz orbital and pz orbital**:
- When two pz orbitals are aligned along the z-axis, they can overlap directly. This head-on overlap will also lead to the formation of a sigma bond.

- **Option D: px orbital and py orbital**:
- The px and py orbitals are oriented along the x and y axes, respectively. Since they are perpendicular to each other and do not overlap directly, they cannot form a sigma bond.

3. **Conclusion**:
- The only pair of orbitals that will not form a sigma bond due to lack of direct overlap is the px orbital and py orbital. Therefore, the correct answer is **Option D**.

### Final Answer:
**Option D: px orbital and py orbital will not form a sigma bond after overlapping.**