The highest known oxide for iron is Fe₂O₃, and no higher oxides are known beyond Group 7. Although ferrates (VI) are formed in alkaline media, they readily decompose to Fe₂O₃ and O₂.

Oxygen’s ability to stabilize the highest oxidation state is evident in oxides, with the highest oxidation number coinciding with the group number, observed in Sc₂O₃ to Mn₂O₇.

The low third ionization enthalpy in Zn is due to the removal of one 4s electron, resulting in a stable d¹⁰ configuration. Removing electrons from d⁵ (Mn²⁺) and d¹⁰ (Zn²⁺) ions is challenging, leading to high third ionization enthalpies.

The high third ionization enthalpies of copper, nickel, and zinc indicate the difficulty in removing additional electrons, limiting their oxidation states to values not greater than two.

The low value for Sc reflects the stability of Sc³⁺, which possesses a noble gas configuration, highlighting the preference for achieving noble gas stability in its oxidation states.