Calculate the formal chrage on each O-atom of O3 molecule.
The Lewis structure of O3 may be drawn as:

The atoms have been numbered as 1, 2 and 3. Formal charge (F.C.) on end O–atom numbered 1.

Formal charge (F.C.)on central O-atom numbered.

Formal charge (F.C.) on end O-atom numbered 3.

Hence, we represent O3 along with the formal charges as follows:
