The correct answer is Ultraviolet radiation.Concept:Ozone layer:It is a layer of ozone molecules found in the stratosphere (the second layer of the atmosphere).Ozone is a molecule made up of three oxygen atoms, often referenced as O3.Explanation:Formation of Ozone:Ozone is formed naturally by chemical reactions involving solar ultraviolet radiation (sunlight) and oxygen molecules.In the first step, solar ultraviolet radiation breaks apart one oxygen molecule (O2) to produce two oxygen atoms (O)In the second step, each of these highly reactive atoms combines with an oxygen molecule to produce an ozone molecule (O3).These reactions occur continually whenever solar ultraviolet radiation is present in the stratosphere.