Answer: a. Elemental iron (Fe) : 0
b. Elemental oxygen
: 0
c. One iron atom in
: +3
d. One oxygen atom in
: -2
Explanation:
Oxidation reaction is defined as the reaction in which a substance looses its electrons. The oxidation state of the substance increases.
Reduction reaction is defined as the reaction in which a substance gains electrons. The oxidation state of the substance gets reduced.
In neutral ionic compound , the oxidation states are exchanged to give the molecular formula. Thus in
iron has oxidation state of +3 and oxygen has oxidation state of -2.
For the reaction :

On reactant side:
Oxidation state of iron in elemental state = 0
Oxidation state of oxygen = 0
On product side:
Oxidation state of iron = +3
Oxidation state of oxygen = -2