(A) is the correct option.Lanthanoids consist of $14$ elements starting from Cerium $(Z = 58)$ to Lutetium $(Z = 71)$.These elements are characterized

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$14$ elements in the sixth period (atomic no. $= 58$ to $71$) that are filling $4f$ sublevel

(A) is the correct option.Lanthanoids consist of $14$ elements starting from Cerium $(Z = 58)$ to Lutetium $(Z = 71)$.These elements are characterized by the progressive filling of the $4f$ orbitals.They are placed in the sixth period of the periodic table and are shown in a separate row at the bottom of the table.

Class 12 Chemistry The d- and f-Block Elements Lanthanoids and Actinoids

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Lanthanoids are

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A
$14$ elements in the sixth period (atomic no. $= 58$ to $71$) that are filling $4f$ sublevel
B
$14$ elements in the seventh period (atomic no. $= 58$ to $71$) that are filling $4f$ sublevel
C
$14$ elements in the sixth period (atomic no. $= 90$ to $103$) that are filling $4f$ sublevel
D
$14$ elements in the seventh period (atomic no. $= 90$ to $103$) that are filling $4f$ sublevel