Is ozone an element or compound

Elements are the simplest substances in nature. There are around 90 naturally occurring elements on earth. They cannot be broken down into anything simpler by physical or chemical means. They consist of only one kind of atom and they can exist as either atoms (eg. argon, calcium, aluminium) or molecules (oxygen, nitrogen).

A compound is formed when two or more elements chemically combine together.

 The elements react chemically and form chemical bonds between the atoms of the elements. In compounds the constituent elements are always present in fixed proportions and therefore a compound has a definite chemical composition.

Ozone is a compound because it is forms by the reaction of oxygen with nascent oxygen.