Question

Lanthanoids are

• A. 14 elements in the sixth period(atomic number = 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 4f-sublevel
• D. 14 elements in the seventh period(atomic number = 58 to 71) that are filling 4f-sublevel

Answer 1

The correct option is C 14 elements in the sixth period(atomic number = 58 to 71) that are filling 4f-sublevel

Lanthanides (58Ce- 71Lu) - This series starts from Lanthanum ( atomic numbe r= 57) and continues up to Lu (Lutetium) as shown in the table above. All the elements of the lanthanide series resemble each other very closely due to the presence of the same number of electrons in the outermost and the penultimate shells. They are also called rare earth elements. Though Lanthanum is a d-block element it is included in the lanthanides series as it resembles them.