Ozone is a highly reactive and unstable form of oxygen.Ozone is made up of three oxygen atoms together, written as O3. It is called activated tri-atomic oxygen. It is a gas and is denser than air. Ozone is the second most powerful sterilizer in the world and its function is to destroy bacteria, viruses and odors. Ozone is nature's way of purifying the air we breathe. Ozone derives from the Greek word ozein, which means to smell. If natural ozone ceased to exist, life on this planet would also cease to exist.