It's not clear what you mean by "3 for ozone". Could you please clarify your question?

Do you mean:

* The 3 main uses of ozone?

* The 3 main ways ozone is formed?

* The 3 main layers of the ozone layer?

* The 3 main contributors to ozone depletion?

Once you clarify your question, I can give you a more specific and helpful answer.