BCl₃ does not exist as dimer but BH₃ exists as dimer (B₂H₆) because

• A

  Chlorine is more electronegative than hydrogen

• B

  There is ${\mathrm{p}}_{\mathrm{\pi }}-{\mathrm{p}}_{\mathrm{\pi }}$ back bonding in BCl₃, but BH₃ does not contain such multiple bonding

• C

  Large-sized chlorine atoms do not fit in between the small boron atoms, whereas small-sized hydrogen atoms fit between boron atoms

• D

  None of these