Which element has the electron configuration [Ar] 4s² 3d⁵?

The electron configuration [Ar] 4s² 3d⁵ corresponds specifically to the element manganese. This configuration can be analyzed by breaking it down into its components.

The notation [Ar] indicates that the electron configuration starts from the argon core, which accounts for the first 18 electrons. After argon, the configuration indicates that there are 2 electrons in the 4s subshell and 5 electrons in the 3d subshell. Manganese, with an atomic number of 25, has a total of 25 electrons, which aligns perfectly as it encompasses the 18 electrons from argon, 2 from the 4s subshell, and 5 from the 3d subshell, thus totaling 25 electrons.

This configuration is characteristic of manganese, as it represents the filling order of the orbitals consistent with the Aufbau principle. Understanding this helps confirm that manganese's 3d subshell can accommodate up to 10 electrons, and in its neutral state, it has precisely 5, which contributes to its unique properties and chemical behavior.

Elements like cobalt, nickel, and iron have different configurations; cobalt, for example, has an electron configuration ending in 4s² 3d