Question

What are the oxidation states of the ferric ion and ferrous ion?

Answer 1

We know that oxidation state which is also referred to as oxidation number is defined as the total number of electrons that an atom gains or loses in order to form a chemical bond with another atom. It reflects the ability to acquire, donate or share electrons within a chemical reaction.

Complete answer:
Iron is a chemical element with atomic number 26 and represented by symbol Fe. It belongs to group 8 of the periodic table and is present in the first transition series. As it is a transition metal, so it has a tendency to exist in variable oxidation states which are discussed below:
Atomic number of Fe $= 26$
Electronic configuration at ground state $= [Ar]3{d^6}4{s^2}$
Iron in its $+ 2$ oxidation state:
When Fe atom donate electrons from its valence shell i.e., from $4s$ subshell, then it acquires a charge of $+ 2$ and the electronic configuration of the atom can be represented as follows:
$F{e^{2 + }} = [Ar]3{d^6}$
Iron in its $+ 2$ oxidation state is known as ferrous ions and can be formed by the reduction of ferric ions.
Iron in its $+ 3$ oxidation state:
When Fe atom donate electrons from its valence shell i.e., from $4s$ subshell as well as one paired electron from d-subshell in order to form stable half-filled d subshell, then it acquires a charge of $+ 3$ and the electronic configuration of the atom can be represented as follows:
$F{e^{3 + }} = [Ar]3{d^5}$
Iron in its $+ 3$ oxidation state is known as ferric ion and can be formed by the oxidation of ferrous ions.
Thus, we can conclude that the oxidation states of the ferric ion and ferrous ion are $+ 3$ and $+ 2$ respectively.

Note:
It is important to note that ferrous ion is relatively less stable than ferric ion because ferric ion i.e., iron atom in its $+ 3$ oxidation state forms a highly stable half-filled d subshell. Remember that ferrous ion is a good reducing agent whereas ferric ion acts as an oxidizing agent.