An investigation shows that for every chlorine atom generated from a fluoro  halogenoalkane in the stratosphere, one hundred thousand atoms of ozone may be destroyed. Which of the following statements about chlorine atoms helps to explain this?

Fluorohalogenoalkane (e.g. CFCs) in the stratosphere decomposes in the presence of u.v. light to give chlorine free radicals, which then attack zone  in a chain reaction. The reaction of the chlorine monoxide radical with an oxygen atom results in the formation of another chlorine radical, which can then start the chain reaction over again. The net result each time a molecule of ozone reacts with a chlorine radical is the destruction of a molecule of ozone.