Sentence:  The reaction rates observed at 200 ` ranged from * * f of the <WSD>chlorine</WSD> exchanged per hour to 0.7 exchanged per hour . 
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)