Which of the following is the best order of Lewis acid strength of BF3, BCl3 and BBr3 ?

(a) BF3 > BCl3 > BBr3

(b) BF3 = BCl3 > BBr3

(c)BF3 < BCl3 < BBr3

(d) BBr3 > BF3 > BCl3

(c)

Sol. 2p of Boron will overlap with 2p of F most efficiently. Hence, BF3 is having the least tendency to accept the lone pair from an external source.