Which of the following will result in zero overlap if molecular axis is `x-`axis ?

Options

A. `1s - 2p_(x)`
B. `2s - 2p_(z)`
C. `2p_(x) - 2p_(x)`
D. `1s - 2p_(y)`

Explanation

To determine which pairs of orbitals will result in zero overlap when the molecular axis is aligned with the x-axis, we need to analyze the orientation of the orbitals involved.

### Step-by-Step Solution:

1. **Understanding Orbital Orientation**:
- The molecular axis is defined as the x-axis. We need to consider how different types of orbitals orient themselves in relation to this axis.

2. **Analyzing Each Pair**:
- **Pair 1: 1s and 2px**:
- The 1s orbital is spherical and can overlap with the 2px orbital, which is oriented along the x-axis. Thus, they can overlap effectively. **(Not zero overlap)**

- **Pair 2: 2s and 2pz**:
- The 2s orbital is spherical, while the 2pz orbital is oriented along the z-axis (perpendicular to the x-axis). Since these orbitals do not approach each other in the x-direction, they do not overlap. **(Zero overlap)**

- **Pair 3: 2px and 2px**:
- Both orbitals are oriented along the x-axis. Therefore, they can overlap effectively. **(Not zero overlap)**

- **Pair 4: 1s and 2py**:
- The 1s orbital is spherical, while the 2py orbital is oriented along the y-axis (perpendicular to the x-axis). Since these orbitals do not approach each other in the x-direction, they do not overlap. **(Zero overlap)**

3. **Conclusion**:
- The pairs that result in zero overlap when the molecular axis is the x-axis are:
- 2s and 2pz
- 1s and 2py

### Final Answer:
The correct options that result in zero overlap are **2s and 2pz (Option B)** and **1s and 2py (Option D)**.

---