Step-by-step explanation:
Lewis acid-base reaction involves the donation of lone pair electrons from base to acid.
The Lewis acid is the electron pair acceptor; the Lewis base is the electron pair donor.
(a) SO32- Lewis acid Lewis base
A Lewis base must contain at least one lone pair of electrons. All anions are typically Lewis bases.
(b) SO3 Lewis acid Lewis base
Lewis acids are electron pair acceptor, the sulfur atom in SO3 has only three electron regions - it is electron deficient, which makes SO3 Lewis acidic.
(c) Mg2+ Lewis acid Lewis base
Mg2+ is a cation which is an electron pair acceptor, and thus a Lewis acid.
(d) BeCl2 Lewis acid Lewis base
Lewis acids are electron pair acceptors. Since the central beryllium atom in BeCl2 has four electrons around it, it still has room to accept more. BeCl2 is a lewis acid.