Arrange the following in the correct order of Lewis acidity: BF 3 , BCl 3 , BBr 3 .

1. BF₃ > BBr₃ > BCl₃
2. BF₃ > BCl₃ > BBr₃
3. BF₃ < BCl₃ < BBr₃
4. BBr₃ < BF₃ < BCl₃

Solution

In BF₃, BCl₃ and BBr₃ each will shown ${\text{p}}_{\pi }-{\text{p}}_{\pi }$ back bonding as follows.



Extant of overlapping  as the $2\text{p}-2\text{p}>2\text{p}-3\text{p}>2\text{p}-4\text{p} \;$ difference between the size of p orbital increases the extent of overlapping decreases the availability of vacant orbital increases and the acidic character increases. 
Hence correct order of Lewis acidity represented by option (BF₃ < BCl₃ < BBr₃) .

Asked in: MHT CET Full Test 13

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