Assertion : Bond dissociation energy of `B-F` bond in `BF_(3)` molecule is lower than `C-F` bond in `CF_(4)` molecule.
Reason : Atomic size of B-atom is larger than that of C-atom.

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

Answer

To solve the question regarding the assertion and reason about the bond dissociation energy of the B-F bond in BF3 compared to the C-F bond in CF4, we can break it down step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the bond dissociation energy of the B-F bond in BF3 is lower than that of the C-F bond in CF4.
- Bond dissociation energy refers to the amount of energy required to break a bond between two atoms.

2. **Analyzing BF3 and CF4**:
- BF3 (Boron Trifluoride) has boron bonded to three fluorine atoms.
- CF4 (Carbon Tetrafluoride) has carbon bonded to four fluorine atoms.

3. **Bond Strength Comparison**:
- In BF3, boron is electron-deficient and can engage in back-bonding with fluorine. This back-bonding involves the donation of electron density from fluorine to boron, which strengthens the B-F bond.
- In CF4, carbon uses sp3 hybridization to bond with fluorine. There is no significant back-bonding in CF4, making the C-F bond relatively weaker compared to the B-F bond in BF3.

4. **Conclusion on Assertion**:
- Since the B-F bond benefits from back-bonding, it is actually stronger than the C-F bond. Therefore, the assertion that the bond dissociation energy of B-F in BF3 is lower than that of C-F in CF4 is **false**.

5. **Understanding the Reason**:
- The reason states that the atomic size of the boron atom is larger than that of the carbon atom.
- This statement is true. As we move across a period in the periodic table, atomic size decreases due to increased nuclear charge, which pulls electrons closer to the nucleus.

6. **Conclusion on Reason**:
- The reason provided is true, but it does not support the assertion since the assertion itself is false.

7. **Final Evaluation**:
- Since the assertion is false and the reason is true, the correct conclusion is that the assertion and reason are not related in a way that supports each other.

### Final Answer:
- The assertion is false, and the reason is true. Therefore, the correct option is that the assertion is incorrect while the reason is correct.