Why does iron have no oxidation state corresponds to loss of all it's valence electrons?

When an element loses an electron, its oxidation number increases.

Explanation:

The oxidation number of an element indicates the hypothetical charge of an atom in a compound. It is hypothetical because, in the context of a compound, the elements may not necessarily be ionic. When the number of electrons associated with an atom changes, its oxidation number also changes. When an element loses an electron, its oxidation number increases.

level 4 to level 2 : ))