Question

Lanthanides are

• A. 14 elements in the sixth period (atomic no. = 90 to 103) that are filling 4f sub-level
• B. 14 elements in the seventh period (atomic no. = 90 to 103) that are filling 5f sub-level
• C. 14 elements in the sixth period (atomic no.= 58 to 71) that are filling 4f sub-level
• D. 14 elements in the seventh period (atomic no. = 58 to 71) that are filling 4f sub-level

Answer 1

Answer: (C)

Lanthanides are the $14$ elements of IIIB group and sixth period ( At. no. = $58$ to $71$ ) that are filling $4 f$ sub-shell of antipenultimate shell from $1$ to $14$. Actually, they are placed below the periodic table in horizontal row as lanthanide series.