`BCl_(3)` does not exist as dimer but `BH_(3)` exist as dimer `(B_(2)H_(6))` because :-
A. Chlorine is more electronegative than hydrogen
B. There is `p_(pi)-p_(pi)` bonding in `BCl_(3)` but `BH_(3)` does not contain such bonding
C. Large sized chlorine atoms do not fit between the small boron atoms whereas smalled sized hydrogen atoms get fitted between boron aotms.
D. None of these
