Free radicals are chemical species that contain a singly occupied orbital. They are neutral and tend to be highly reactive. These are formed by homolytic cleavage of covalent bonds. These have high tendency to pair the unpaired electron. These readly combine with each other or with other molecules to pair their electrons. In a free radical reaction, free readily is formed as reaction intermediate. It is the reaction which involves free radicals. These reactions take place mainly in the presence of UV light.