What are Lanthanoids?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 14 elements in the VI period (atomic number = 58 to 71) that are filling the 4f-sublevel
The lanthanoids are the fourteen elements after lanthanum, from cerium (Z = 58) to lutetium (Z = 71). Their outermost shell is 6s, so they belong to the sixth period, and the electrons added along the series enter the 4f level.
NCERT (2026-27 edition):
Unit 4 The d- and f-Block Elements – “… The two series of the inner transition metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as lanthanoids and actinoids respectively.”
The Inner Transition Elements (f-Block) – “The f-block consists of the two series, lanthanoids (the fourteen elements following lanthanum) and actinoids (the fourteen elements following actinium).”
4.5.1 Electronic Configurations – “It may be noted that atoms of these elements have electronic configuration with 6s2 common but with variable occupancy of 4f level (Table 4.9).”
