Iron is a transition metal with an atomic number of 26.
What is the ground-state electronic configuration of the iron(II) ion, Fe2+\text{Fe}^{2+}Fe2+?
1s22s22p63s23p63d44s21s^2 2s^2 2p^6 3s^2 3p^6 3d^4 4s^21s22s22p63s23p63d44s2
1s22s22p63s23p63d61s^2 2s^2 2p^6 3s^2 3p^6 3d^61s22s22p63s23p63d6
1s22s22p63s23p63d54s11s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^11s22s22p63s23p63d54s1
1s22s22p63s23p63d64s21s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^21s22s22p63s23p63d64s2
