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Halogens is the common name for five elements (fluorine, chlorine, bromine, iodine and astatine) that belong to group VII A of the Periodic Table. They are all characterized by having one electron missing in their outermost valence shell which makes them strongly electronegative and good oxidizing agents. At room temperature and pressure, fluorine and chlorine are diatomic gazes, bromine is a reddish-brown liquid, while iodine and astatine are solids. They are highly toxic, while fluorine, chlorine and bromine also present a fire risk.

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