Final answer:
The condensed noble-gas electron configuration for Fe²⁺ is [Ar] 3d⁶, as it loses two electrons from the 4s orbital when forming the ion.
Step-by-step explanation:
The condensed noble-gas electron configuration of Fe²⁺ is written by first indicating the electron configuration of the nearest noble gas with a lower atomic number, which is Argon (Ar). Then we add the electrons in the orbitals beyond that. For iron (Fe), which has an atomic number of 26, the electron configuration would normally be [Ar]4s² 3d⁶. However, when it loses two electrons to form Fe²⁺, the electrons are removed first from the 4s orbital, thus giving us [Ar] 3d⁶ for the Fe²⁺ ion.