Question

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

• A. Chlorine is more electronegative than hydrogen
• B. There is a $p\pi -p\pi$ back bonding in $BC{l}_3$ but $B{H}_3$ does not contain such bonds
• C. Large sized chlorine atoms do not fit in between the boron atoms whereas small sized hydrogen atoms fit in between the boron atoms
• D. None of the above

Answer 1

The correct option is C Large sized chlorine atoms do not fit in between the boron atoms whereas small sized hydrogen atoms fit in between the boron atoms

$BC{l}_3$ does not exist as dimer but $B{H}_3$ exists as dimer ($B_2{H}_6$) because, large sized chlorine atoms do not fit in well between the small boron atoms. Whereas the smaller sized hydrogen atoms can well fit in between the boron atoms.