`BCl_(3)` does not exists as a dimer but `BH_(3)` exists as `B_(2)H_(6)` because :
A. Chlorine is more electronegative than hydrogen.
B. Large size of chlorine atom does not fit between small-sized boron atoms, while small-sized hydrogen atoms occupy the space between boron atoms.
C. There is `p pi - p pi` back bonding in `BCl_(3)`.
D. Both (b) and ( c).
