Assertion : If `d_(x^(2)-y^(2)) and p_(y)` orbitals come close together along z-axis, they can form `pi-` bond by sideways overlapping.
Reason : Both oritals do not electron density along z-axis.

Options

A. If assertion is true but the reason is false
B. If assertion is false but reason is true
C. If both assertion and reason are true and the reason is the correct explanation of assertion
D. If both assertion and reason are true and the reason is not the correct explanation of assertion

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the `d_(x^2 - y^2)` and `p_y` orbitals can form a `pi` bond when they come close together along the z-axis due to sideways overlapping.
- The `d_(x^2 - y^2)` orbital has its electron density concentrated along the x and y axes, while the `p_y` orbital has its electron density along the y-axis.

**Hint**: Consider the orientation of the orbitals and how they interact with each other.

2. **Analyzing the Orbital Orientation**:
- The `d_(x^2 - y^2)` orbital is oriented in such a way that it has lobes along the x and y axes, meaning it does not have any electron density along the z-axis.
- The `p_y` orbital, on the other hand, has its lobes oriented along the y-axis, with no electron density along the z-axis.

**Hint**: Visualize the shapes of the orbitals to understand their orientations better.

3. **Evaluating the Possibility of Bond Formation**:
- For a `pi` bond to form, there must be a sideways overlap of orbitals. However, since both the `d_(x^2 - y^2)` and `p_y` orbitals lack electron density along the z-axis, they cannot effectively overlap in that direction.
- Therefore, the assertion that they can form a `pi` bond along the z-axis is incorrect.

**Hint**: Recall the requirements for `pi` bonding and the significance of orbital overlap.

4. **Understanding the Reason**:
- The reason states that both orbitals do not have electron density along the z-axis, which is indeed true.
- The `d_(x^2 - y^2)` orbital has its density along the x and y axes, while the `p_y` orbital has its density along the y-axis only.

**Hint**: Confirm the electron density distribution of both orbitals.

5. **Conclusion**:
- Since the assertion is false (they cannot form a `pi` bond), but the reason is true (both orbitals do not have electron density along the z-axis), the correct answer is that the assertion is false and the reason is true.

### Final Answer:
- Assertion: False
- Reason: True
- Therefore, the correct option is that the assertion is false, but the reason is true.