Which one of the following species represents ozone?

The species that represents ozone is O3. Ozone is a triatomic molecule composed of three oxygen atoms bonded together, which distinguishes it from dioxygen (O2), which is diatomic and consists of two oxygen atoms. Ozone has unique properties and plays a crucial role in the atmosphere, particularly in the stratosphere where it forms the ozone layer that protects life on Earth by absorbing the majority of the sun's harmful ultraviolet radiation.

The other species mentioned are different compounds: O2 is the molecular form of oxygen that humans and animals breathe, NO2 is nitrogen dioxide, a pollutant and a product of combustion, and N2O is nitrous oxide, commonly known as laughing gas. Each has its own distinct molecular structure and function, which highlights the specificity of ozone's representation as O3.