Question

Lanthanoids are

(a) A elements in the sixth period (atomic no. 90 to 103) that are filling 4f sublevel

(b) 14 elements in the seventh period (atomic number = 90 to 103) that are filling 5f sublevel

(c) 14 elements in the sixth period (atomic number = 58 to 71) that are filling the 4f sublevel

(d) 14 elements in the seventh period (atomic number = 50 to 7l) that are filling 4f sublevel.

Answer 1

Correct option (c) 14 elements in the sixth period (atomic number = 58 to 71) that are filling the 4f sublevel

Explanation :

As sixth period can accommodate only 18 elements in the table, 14 members of 4f series (atomic number 58 to 71) are separately accommodated in a horizontal row below the periodic table. These are called as lanthanides.