The group of elements in which the differentiating electron enters the prepenultimate shell of atoms is called:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → f-Block elements
The differentiating electron is the last electron, the one by which an element differs from the one before it. In the f-block elements it enters the (n−2)f orbitals, i.e. the shell two below the outermost one (the prepenultimate or antepenultimate shell). Their general configuration is (n−2)f1–14(n−1)d0–1ns2, which is why they are also called the inner transition elements.
Why the other options are incorrect
Option (1) s-Block elements — Incorrect. The differentiating electron enters the ns orbital of the outermost shell.
Option (2) p-Block elements — Incorrect. The differentiating electron enters the np orbitals of the outermost shell.
Option (3) d-Block elements — Incorrect. The differentiating electron enters the (n−1)d orbitals, the penultimate shell.