Sentence:  Furthermore , the exchange would not be expected to be sensitive to trace amounts of impurities because it would not be apt to be a chain reaction since the activation energy for abstraction of chlorine by a <WSD>chlorine</WSD> atom would be expected to be too high ; also it would be expected that * * f would compete very effectively with any impurities as a scavenger for * * f radicals . 
Meaning of the word marked with <WSD> tags:  a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)