23V=1s22s22p6,3s23p63d3,4s2 24V=1s22s22p6,3s23p63d5,4s1 26V=1s22s22p6,3s23p63d6,4s2 25V=1s22s22p6,3s23p63d5,4s2 Third electron which is removed in third ionisation enthalpy belongs to 3d-subshells, It means in all elements, shell and subshells are same therefore, required amount of energy is based upon stability of d subshell. Hence, Mn shows highest third ionisation energy.