Answer:
Ozone, 3.
Step-by-step explanation:
Ozone is a molecule of oxygen with 3 oxygen atoms instead of 2 that is present in the atmosphere of the earth. It is a very important gas because this gas filter the solar radiation from ultra violet radiation which causes skin cancer disease. Ozone is present in the stratosphere layer of atmosphere that is present between 15 to 30 kilometer high from the earth surface.