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                                    Lanthanides areA. 14 elements in the sixth period (At.no=90 to 103) that are filling 4f sub-levelB. 14 elements in the seventh period (At.no.=90 to 103) that are filling 5f sub-levelC. 14 elements in the sixth period (At.no.=58 to 171) that are filling 4f sub-level).D. 14 elements in the seventh period (At. No.=58 to 71) that are filling 4f sub-level | 
                            
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Answer» Correct Answer - C Lanthanides are the 14 elements of IIIB group and sixth period (at no. =58 to 71) that are filling sub-shell of antipenultimate shell from 1 to 14. Actually, they are placed below the periodic table horizontal row as lanthanide series.  | 
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