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 the : smaller size of B atom as compared to that of C atom.; stronger `sigma` bond between B and F in `BF_3` as compared to that between C and F in `CF_4`; significant `p pi-p pi` interactions between B and F in `BF_3`, whereas there is no possibility of such interaction between C and F in `CF_4`; lower degree of `p pi-p pi` interactions between B and F in `BF_3` than that between C and F in `CF_4`

Options

A. smaller size of B atom as compared to that of C atom
B. stronger `sigma` bond between Band F in `BF_3` as compared to that between C and F in `CF_4`.
C. significant `p pi- p pi` interactions between B and F in `BF_3` , whereas there is no possibility of such interaction between C and F in `CF_4`
D. lower degree of `ppi -p pi` interactions between B and F in `BF_3` than that between C and F in `CF_4`

Answer

C

Explanation

Bond strength of B-F bond is higher in BF, as compared to C-F bond in CF, due to formation of extra `p pi - p pi` bond between B and F. `p pi - p pi` bonding is not possible in `CF_4`