Choose the Incorrect statement from the following:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → All the lanthanoids are hard metals
The lanthanoids are silvery-white soft metals that tarnish rapidly in air. Their hardness increases with atomic number, and samarium is steel hard.
Option (1) Two series of f-block; lanthanoids and actinoids collectively consists of twenty eight elements. — A correct statement. The lanthanoids are the 14 elements from Ce (58) to Lu (71), and the actinoids are the 14 elements from Th (90) to Lr (103), which makes 28 in all.
Option (2) All the lanthanoids are hard metals — The incorrect statement. The lanthanoids are silvery white soft metals. Their hardness increases with atomic number, and samarium is steel hard, but the group as a whole is not hard.
Option (3) Actinoid contraction is greater from element to element than lanthanoid contraction — A correct statement. 5f electrons shield the outer electrons from the nuclear charge even more poorly than 4f electrons, so the size falls more sharply from one actinoid to the next.
Option (4) Actinoids show a greater range of oxidation states than lanthanoids — A correct statement. In the actinoids the 5f, 6d and 7s levels are close in energy, so many electrons can take part in bonding (Np and Pu reach +7). The lanthanoids mainly show +3, with +2 and +4 in only a few cases.
NCERT (2026-27 edition):
General Characteristics
