Sentence:  It appears possible to set a lower limit of about * * f for the activation energy of the abstraction of a chlorine atom from a carbon tetrachloride molecule by a <WSD>chlorine</WSD> atom to form * * f radical . 
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)