Third ionization energy of manganese greater than chromium and iron?

Question

Manganese: [Ar] 4s2 3d5

Chromium: [Ar]4s1 3d5

Iron: [Ar]4s2 3d6

The question is:

Using the electron configurations, why is the third ionization energy of manganese greater than those of both chromium and iron?

Answer 1

The discussion is about the ionization potentials of:

Mn(2+): [Ar] 4s0 3d5

Cr(2+): [Ar]4s0 3d4

and Fe(2+): [Ar]4s0 3d6

Since Mn(2+), with its electron configuration [Ar] 4s0 3d5, has the 3d orbital half filled, it is more stable than both Cr(2+) ([Ar]4s1 3d5) and Fe(2+) ([Ar]4s2 3d6).  Therefore its ionization energy of Mn(2+) would be the highest among these three.

Note: Half filled d-orbitals are less stable than completely filled, but more stable than all the others.