Question

which is the strongest Lewis acid a-bf3 b-bcl3 c-bi3 d-bbr3

Answer 1

A boron is electro deficient and the F is trying to attract elctrons toward itself.

And as Lewis acid means proton acceptor

Due to less electron density on B

BF3 would be the strongest Lewis acid.

Hope this helps

Answer 2

Strongest Lewis acid is

BBr3.
due to empty P orbital,boron is involved to greater extent in "n" bonding.
so BBr3 is considered as strongest Lewis acid.
Hope this helps you.