Question

Which of the following is the strongest Lewis acid?

• A. $BF_{3}$
• B. $BCl_{3}$
• C. $BBr_{3}$
• D. $BI_{3}$

Answer 1

Answer: (D)

$BI_{3}$

Answer 2

The order of acid strength of Lewis acids, (i.e., boron trihalides) is as:
$B I_{2}>B B r_{3} >B C l_{3}>B F_{3}$ because the acid strength increases with increasing atomic size (or going down in periodic table.)