The bond dissociation energy of `B-F` in `BF_(3)` is `"646 kJ mol"^(-1)` whereas that of `C-F` in `CF_(4)` is `"515 kJ mol"^(-1)`. The correct reason for higher `B-F` bond dissociation energy as compared to that of `C-F` is

Options

A. stonger `sigma` bond between B and F in `BF_(3)` as compared to that between C and F in `CF_(4)`
B. significant `ppi-ppi` interaction between B and F in `BF_(3)` whereas there is no possibility of such interaction between C and F I `CF_(4)`
C. lower degree of `ppi-ppi` interaction between B and `F BF_(3)` than that between C and F `CF_(4)`
D. smaller size of B - atom as compared to that of C - atom

Answer

To determine the reason for the higher bond dissociation energy of the B-F bond in BF₃ compared to the C-F bond in CF₄, we can analyze the bonding and electronic structure of both molecules.

### Step-by-Step Solution:

1. **Understanding Bond Dissociation Energy**:
- Bond dissociation energy is the energy required to break a bond in a molecule. A higher bond dissociation energy indicates a stronger bond.

2. **Analyzing BF₃**:
- In BF₃, boron (B) has three fluorine (F) atoms bonded to it. Boron has only three valence electrons and forms three covalent bonds with fluorine, resulting in a total of six electrons around boron (not a complete octet).
- Due to the incomplete octet, boron can engage in back-bonding with fluorine. This means that the lone pairs of electrons on the fluorine atoms can interact with the empty p-orbitals of boron, effectively forming a double bond character in the B-F bond.

3. **Analyzing CF₄**:
- In CF₄, carbon (C) is bonded to four fluorine atoms. Carbon has four valence electrons and forms four covalent bonds with fluorine, resulting in a complete octet (eight electrons around carbon).
- Since carbon has a complete octet, there is no possibility for back-bonding or any additional stabilization of the C-F bond. The bond remains a single bond.

4. **Comparing B-F and C-F Bonds**:
- The presence of back-bonding in BF₃ increases the effective bond order of the B-F bond, making it stronger and resulting in a higher bond dissociation energy (646 kJ/mol).
- In contrast, the C-F bond in CF₄, being a single bond without any back-bonding, has a lower bond dissociation energy (515 kJ/mol).

5. **Conclusion**:
- The higher bond dissociation energy of the B-F bond compared to the C-F bond is primarily due to the presence of back-bonding in BF₃, which increases the bond strength.

### Final Answer:
The correct reason for the higher B-F bond dissociation energy as compared to that of C-F is due to back-bonding in BF₃, which increases the bond strength.