Fe(Z=26)→e−=26 Fe2+(Z=26)→e−=24 Electronic configuration: Fe(Z=26)→1s22s22p63s23p63d64s2 Fe2+(z=26)→1s22s22p63s23p63d64s0 as 4s is the outermost shell of Fe that's why e−will always removed first from 4s, so retained e−in d− shell is 6