Question

Which one of the following is strongest Lewis acid ?

• A. $BF_3$
• B. $BCl_3$
• C. $BBr_3$
• D. $BI_3$

Answer 1

Answer: (D)

$BI_3$

Answer 2

The relative strength of Lewis acids of boron trihalide increases in the order $BF_3 < BCl_3 < BBr_3 < BI_3$ This can be explained on the basis of the tendency of the halogen atom to back donate its electron to the boron atom and makes it less electron deficient