`BCl_(3)` doesnot exist as dimer but `BH_(3)` exist as dimer `(B_(2)H_(6))` because

Options

A. chlorine is more electronagative than hydrogen
B. there is `p pi- d pi` back bonding in `BCl_(3)` but `BH_(3)` doesnot contain such multiple bonds
C. large size chlorine atom donot fir in between small boran atoms where as small sized hydrogen atom get fitted in between boran atoms
D. none of the above

Answer

C

Explanation

Small sized boran atom cannot coordinate to four large size chlorine atims.