Question

Compare $B-B$ bond lengths in the following molecules:

• A. $x>y$
• B. $y>x$
• C. $x=y$
• D. None of these

Answer 1

The correct option is B $y>x$

Fluorine is an electron negative element so as per bent's rule more electronegative element will have less % s- character therefore $B-B$ bond will have more % s- character and shorter bond length.
Similarly, in $B_{2}C{l}_6$ chlorine is less elelctronegative hence will have more % s charecter hence the $B-B$ bond angle will have less % s character and hence longer bond length.
The side atom in the 1st case is $F$ which is more electronegative than the side atom chlorine in the 2nd case.