Question

$BC{l}_3$ does not exist as a dimer but $B{H}_3$ exists as a dimer because:

• A. chlorine is more electropositive than hydrogen
• B. there is $p\pi -p\pi$ back-bonding in $BC{l}_3$ but $B{H}_3$ does not contain such multiple bonding
• C. large sized chlorine atoms cannot fit in between small sized boron atoms, whereas small sized hydrogen atoms can easily fit in between boron atoms
• D. None of the above

Answer 1

Answer: (C)

large sized chlorine atoms cannot fit in between small sized boron atoms, whereas small sized hydrogen atoms can easily fit in between boron atoms

$BC{l}_3$ does not exist as a dimer but$B{H}_3$ exists as a dimer because the size of boron is very much smaller than the size of the chlorine.

The dimer of $BC{l}_3$is $B_{2}C{l}_6$, which is not possible as large-sized chlorine atoms cannot fit in between small-sized boron atoms. While small-sized hydrogen atoms can easily fit in between boron atoms.

Hence, the correct option is (C).