2004 AIPMT The d- and f-Block ElementsThe Lanthanoids Easy Question 66 of 76 in The d- and f-Block Elements

Lanthanoids are :-

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

The answer is B.

Solution

The lanthanoids are the 14 elements that follow lanthanum (Z = 57), from cerium (Z = 58) to lutetium (Z = 71).
In these elements the differentiating electron enters the 4f sublevel. General configuration: $[Xe]\,4f^{1-14}\,5d^{0-1}\,6s^2$.
They belong to the sixth period (the period with principal quantum number n = 6 for the outermost shell).
The elements with atomic numbers 90 to 103 (thorium to lawrencium) are the actinoids. They lie in the seventh period and fill the 5f sublevel.
So lanthanoids are 14 elements in the sixth period (atomic no. 58 to 71) that are filling the 4f sublevel.

Concept Position of lanthanoids in periodic table

The d- and f-Block Elements in past papers

76 questions from this chapter have appeared across 27 exam years.