Explanation:

- Ozone is an allotrope of oxygen, which means it is a different form of the same element.

- Oxygen typically exists as O2, but ozone is O3, consisting of three oxygen atoms bonded together.

- ?? Option 2: Oxygen is the correct answer.

- Carbon dioxide (Option 1) is a compound consisting of both carbon and oxygen atoms, not an allotrope.

- Hydrogen (Option 3) has its own allotropes, but ozone is not one of them.

- Nitrogen (Option 4) also has different forms but is unrelated to ozone.