`BCl_(3)` does not exist as dimer but `BH_(3)` exist as dimer `(B_(2)H_(6))` because :-
A. Cl is more electropositive than H
B. Three is `ppi -ppi ` back bonf=ding in `BCl_(3)` but `BH_(3)` does not contain such multiple bonding
C. Small sized chlorine atoms do not fit in between small sized boron atoms where as small sized hydeogen atoms get fitted in between boron atoms
D. There is `ppi-dpi` back bonding in `BCl_(3)` but `BH_(3)` does not contain such multiple bonding
