To evaluate which statement is not correct about the lanthanoids, let's examine each option individually for accuracy:

Option A: This statement is correct. The lanthanoids consist of the 14 elements in the sixth period of the periodic table, with atomic numbers 58 (Cerium, Ce) through 71 (Lutetium, Lu). These elements are characterized by the filling of their $$4f$$ sublevel.

Option B: This statement is also correct. The most common oxidation state of lanthanoids is +3. This is because in this oxidation state, they tend to lose their three outer electrons (two from the $$6s$$ sublevel and one from the $$4f$$ or $$5d$$ sublevels) to achieve a more stable electronic configuration.

Option C: This statement is not correct. Although the availability of $$4f$$-electrons does indeed allow for a variety of oxidation states among the lanthanoids, not all elements in the series form compounds in a +4 oxidation state. While certain lanthanoids like Cerium (Ce) can exhibit a +4 oxidation state, it is not a general characteristic for all elements in the series. Different lanthanoids have different capacities to achieve higher oxidation states, and the +4 state is not universally applicable to all lanthanoids.

Option D: This statement is missing an important part of the information that seems to have been cut off. The statement likely refers to the "lanthanide contraction," which is the gradual decrease in atomic and ionic radii of the lanthanoid elements with increasing atomic number. This phenomenon is due to the imperfect shielding of nuclear charge by the $$4f$$ electrons, leading to a stronger attraction between the nucleus and the outer electrons, resulting in smaller atomic sizes. Assuming the statement intended to reference the lanthanide contraction, it would be correct assuming proper context was given.

Therefore, Option C is the statement that is not correct in the context of the lanthanoids.

Physical Chemistry

Inorganic Chemistry

Organic Chemistry

d and f Block Elements · Chemistry · VITEEE

MCQ (Single Correct Answer)