Mn+ has 3d54s1 configuration and
configuration of Cr+ is d5, therefore, ionisation enthalpy of Mn+ is lower
than Cr+ In the same way, Fe2+ has d6 configuration and Mn2+ has 3d5
configuration Hence, ionisation enthalpy of Fe2+ is lower than the Mn2+ In other words, we can say that the third ionisation enthalpy of Fe is
lower than that of Mn