Chemistry · D and f Block Elements

The correct answer is Fe²⁺. The electron configuration for Fe²⁺ is [Ar] 3d⁶, with the 3d subshell holding six electrons: four of these are unpaired due to Hund's rule, which states that electrons fill degenerate orbitals singly first. Mg²⁺ lacks d electrons entirely, Ti³⁺ has only one unpaired d electron ([Ar] 3d¹), and V³⁺ has two unpaired d electrons ([Ar] 3d²).

Mg²⁺ has the electron configuration 1s² 2s² 2p⁶. It lacks d electrons entirely, resulting in no unpaired d electrons.

Ti³⁺ has the electron configuration [Ar] 3d¹, meaning it contains only one unpaired d electron.

V³⁺ has the electron configuration [Ar] 3d². It has two unpaired d electrons, following Hund's rule of maximum multiplicity.

Fe²⁺ has the electron configuration [Ar] 3d⁶. According to Hund's rule, it has four unpaired d electrons, making it the option with the most unpaired d electrons among the given choices.