MCQ
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
  • Significant $p\pi  -p\pi $ interaction between $B$ and $F$ in $BF_3$ whereas there is no possibility of such interaction between $C$ and $F$ in $CF_4$
  • B
    Lower degree of $p\pi  -p\pi $ interaction between $B$ and $F$ in $BF_3$ than that between $C$ and $F$ in $CF_4$
  • C
    Smaller size of $B$ atom as compared to that of $C$ atom
  • D
    Stronger bond between $B$ and $F$ in $BF_3$ as compared to that between $C$ and $F$ in $CF_4$

Answer

Correct option: A.
Significant $p\pi  -p\pi $ interaction between $B$ and $F$ in $BF_3$ whereas there is no possibility of such interaction between $C$ and $F$ in $CF_4$
a
In $BF_3,\, p\pi -p\pi $ back bonding is present

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