A : In Diborane containing eight -B-H bonds only four B-H bonds are on the plane .
R : Boron in `B_(2) H_(6)` is `sp^(2)` hybridised .

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

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 in diborane (B₂H₆), which contains eight B-H bonds, only four B-H bonds are in the same plane.
- To visualize this, we need to draw the structure of diborane. Diborane has a unique structure where two boron atoms are connected by two bridging hydrogen atoms and each boron is also bonded to two terminal hydrogen atoms.
- In the structure, the four terminal B-H bonds lie in the same plane, while the two bridging B-H bonds are above and below this plane, making the overall geometry of diborane a three-dimensional shape.

2. **Conclusion on the Assertion**:
- The assertion is correct because, indeed, only four of the B-H bonds are coplanar while the other four are oriented in a perpendicular manner to this plane.

3. **Understanding the Reason**:
- The reason states that boron in B₂H₆ is sp² hybridized.
- To determine the hybridization of boron in diborane, we need to consider the bonding and geometry. Each boron atom in diborane forms four bonds (two terminal B-H bonds and two bridging B-H bonds).
- Since boron forms four equivalent bonds, it undergoes sp³ hybridization, not sp² hybridization.

4. **Conclusion on the Reason**:
- The reason is incorrect because boron in B₂H₆ is sp³ hybridized due to the formation of four bonds.

5. **Final Conclusion**:
- The assertion is correct, while the reason is incorrect. Therefore, the correct answer is that the assertion is true, and the reason is false.

### Summary:
- **Assertion (A)**: True
- **Reason (R)**: False