▁iron . ▁Mang an ese , ▁like ▁chrom ium ▁before ▁it , ▁is ▁an ▁important ▁component ▁in ▁st ain less ▁steel , ▁prevent ing ▁the ▁iron ▁from ▁rust ing . ▁Mang an ese ▁is ▁also ▁often ▁used ▁in ▁p ig ments , ▁again ▁like ▁chrom ium . ▁Mang an ese ▁is ▁also ▁poison ous ; ▁if ▁enough ▁is ▁in h aled , ▁it ▁can ▁cause ▁irre vers ible ▁ne uro log ical ▁damage . ▁ ▁Iron ▁ ▁Iron ▁( Fe ) ▁is ▁an ▁element ▁in ▁group   8 . ▁Iron ▁is ▁the ▁most ▁common ▁on ▁Earth ▁among ▁elements ▁of ▁the ▁period , ▁and ▁probably ▁the ▁most ▁well - known ▁of ▁them . ▁It ▁is ▁the ▁principal ▁component ▁of ▁steel . ▁Iron - 5 6 ▁has ▁the ▁lowest ▁energy ▁density ▁of ▁any ▁is ot ope ▁of ▁any ▁element , ▁meaning ▁that ▁it ▁is ▁the ▁most ▁massive ▁element ▁that ▁can ▁be ▁produced ▁in ▁super gi ant ▁stars . ▁Iron ▁also ▁has ▁some ▁applications ▁in ▁the ▁human ▁body ; ▁hem og lo bin ▁is ▁partly ▁iron . ▁ ▁Cob alt ▁ ▁Cob alt ▁( Co ) ▁is ▁an ▁element ▁in ▁group   9 . ▁Cob alt ▁is ▁commonly ▁used ▁in ▁p ig ments , ▁as ▁many ▁comp ounds ▁of ▁c ob alt ▁are ▁blue ▁in ▁color . ▁Cob alt ▁is ▁also ▁a ▁core ▁component ▁of ▁many ▁magnetic ▁and ▁high - str ength ▁allo ys . ▁The ▁only ▁stable ▁is ot ope , ▁c ob alt - 5 9 , ▁is ▁an ▁important ▁component ▁of ▁vit amin