Q. The tendency of BF₃, BCl₃ and BBr₃ to behave as Lewis acid decreases in the sequence
A) BF₃ > BCl₃ > BBr₃
B) BCl₃ > BF₃ > BBr₃
C) BBr₃ > BCl₃ > BF₃
D) BBr₃ > BF₃ > BCl₃
Explanation
[Solution from source] Lewis acidity follows how electron-deficient boron remains. Back-donation from the halogen p orbital into boron's empty 2p is strongest for F (similar size 2p–2p) and weakest for Br, so BF₃ is the weakest and BBr₃ the strongest acid: BBr₃ > BCl₃ > BF₃. Going by electronegativity alone wrongly gives BF₃ as strongest. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.