For which of the following orbitals, the electron finding probability is zero, if we move along the z-axis?
(I) `p_x`
(II) `p_y`
(III) `d_z`

Options

A. I and II
B. III
C. I, II and IV
D. I, II and III

Answer

To determine for which of the given orbitals the electron finding probability is zero when moving along the z-axis, we can analyze each orbital one by one.

### Step-by-Step Solution:

1. **Understanding the Orbitals**:
- The orbitals mentioned are `p_x`, `p_y`, and `d_z`.
- Each orbital has a specific orientation in three-dimensional space.

2. **Analyzing the `p_x` Orbital**:
- The `p_x` orbital is oriented along the x-axis.
- When moving along the z-axis, the probability of finding an electron in the `p_x` orbital is zero because this orbital does not extend in the z-direction.

3. **Analyzing the `p_y` Orbital**:
- The `p_y` orbital is oriented along the y-axis.
- Similar to the `p_x` orbital, when moving along the z-axis, the probability of finding an electron in the `p_y` orbital is also zero since it does not extend in the z-direction.

4. **Analyzing the `d_z` Orbital**:
- The `d_z` orbital (often referred to as `d_{z^2}`) has a specific shape that extends in the z-direction.
- Therefore, when moving along the z-axis, there is a non-zero probability of finding an electron in the `d_z` orbital.

5. **Conclusion**:
- The orbitals for which the electron finding probability is zero when moving along the z-axis are `p_x` and `p_y`.

### Final Answer:
The correct orbitals where the electron finding probability is zero along the z-axis are:
- (I) `p_x`
- (II) `p_y`