Four successive members of the first row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionization enthalpy ?

The third ionization enthalpy is the energy required to remove the third electron from an atom. In the first row transition elements, the ionization enthalpy generally increases as we move from left to right due to the increasing effective nuclear charge. However, the third ionization enthalpy is particularly high for elements where the removal of the third electron results in a stable half-filled or completely filled d subshell. Among the given options, manganese (Mn, Z = 25) has a d5 configuration in its second ionized state (Mn3+), which is a stable half-filled d subshell. Removing an electron from this configuration requires more energy, making the third ionization enthalpy of manganese higher than that of its neighbors.