xic ▁in ▁larger ▁quantities . ▁S elenium ▁is ▁a ▁calc ogen . ▁S elenium ▁is ▁red ▁in ▁mon om ol ic ▁structure . ▁But ▁it ▁is ▁met all ic ▁gray ▁in ▁its ▁cry st all ine ▁structure . ▁ ▁B rom ine ▁ ▁B rom ine ▁( Br ) ▁is ▁an ▁element ▁in ▁group   1 7 ▁( hal ogen ). ▁It ▁does ▁not ▁exist ▁in ▁element al ▁form ▁in ▁nature . ▁B rom ine ▁is ▁bare ly ▁liquid ▁at ▁room ▁temperature , ▁bo iling ▁at ▁about ▁ 3 3 0 ▁k el v ins . ▁B rom ine ▁is ▁also ▁quite ▁to xic ▁and ▁cor ros ive , ▁but ▁b rom ide ▁ ions , ▁which ▁are ▁relatively ▁in ert , ▁can ▁be ▁found ▁in ▁hal ite , ▁or ▁table ▁salt . ▁B rom ine ▁is ▁often ▁used ▁as ▁a ▁fire ▁ret ard ant ▁because ▁many ▁comp ounds ▁can ▁be ▁made ▁to ▁release ▁free ▁b rom ine ▁atoms . ▁ ▁K rypt on ▁ ▁K rypt on ▁( K r ) ▁is ▁a ▁noble ▁gas , ▁placed ▁under ▁arg on ▁and ▁over ▁x en on . ▁Being ▁a ▁noble ▁gas , ▁k rypt on ▁rarely ▁interact s ▁with ▁itself ▁or ▁other ▁elements ; ▁although ▁comp ounds ▁have ▁been ▁detected , ▁they ▁are ▁all ▁un stable ▁and ▁decay ▁rapidly , ▁and ▁as ▁such , ▁k rypt on ▁is ▁often ▁used ▁in ▁flu ores cent ▁lights . ▁K rypt on , ▁like ▁most ▁noble ▁g ases , ▁is ▁also ▁used ▁in ▁light ing ▁because