Which of the following is the correct prediction about observed $B-X$ bond length in $BX_3$ molecules?

• A
  $B-F$ bond length in $BF_3$ is found to be less than the theoretical value because electronegativity values of $B$ $(2.04)$ and $F$ $(4.0)$ suggest the bond to be ionic,and hence the attraction between oppositely charged ions must decrease the bond length.
• B
  $BF_3$ and $[BF_4]^-$ have equal $B-F$ bond length.
• C
  The decrease in the $B-F$ bond length in $BF_3$ is due to delocalized $p\pi-p\pi$ bonding between the vacant $2p$-orbital of $B$ and the filled $2p$-orbital of $F$.
• D
  The correct $B-X$ bond length order is $B-F > B-Cl > B-Br > B-I$.