Q. The relative Lewis acid character of boron trihalides is in the order
A) $BI_{3} > BBr_{3} > BF_{3} > BCl_{3}$
B) $BI_{3} > BBr_{3} > BCl_{3} > BF_{3}$
C) $BF_{3} > BCl_{3} > BBr_{3} > BI_{3}$
D) $BCl_{3} > BF_{3} > BI_{3} > BBr_{3}$
Explanation
(b)
$BI_{3} > BBr_{3} > BCl_{3} > BF_{3}$
This order can be easily explained on the basis of the tendency of the halogen atom to back donate its lone pair of electrons to the empty $p$-orbital of the boron atom through $p\pi - p\pi$ bonding.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.