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Q.
The decreasing order of power of boron halides to act as Lewis acids is
The p-Block Elements
Solution:
It is due to $p\pi-p\pi$ back bonding. All halides have lone pairs, they donate one lone pair to boron by overlapping with the p orbital of boron. An effective overlap between orbitals decreases due to the large size of p orbital of halides. Hence, electron deficiency of boron atom in its halides is - $BBr_{3}, > BCL _{3} > BF _{3}$ A species which is more electron deficient will accept electron easily and hence will be more acidic.
