Answer : The correct option is, Oxygen was reduced over the course of this reaction.
Iron rusting : A chemical process in which the an iron nail react with water and oxygen to give iron oxide as a product. Rusting of iron is an oxidation-reduction reaction in which iron losses electrons to oxygen atom.
Oxidation reaction : A substance looses its electrons. In this oxidation state increases.
Reduction reaction : A substance gains electrons. In this oxidation state decreases.
The balanced chemical reaction for rusting of irons is,
Half reactions of oxidation and reduction are :
From this reaction we conclude that the electrons are getting transferred from iron to oxygen. That means in this reaction, oxygen is an oxidizing agent and iron is a reducing agent.
Hence, the correct option is, Oxygen was reduced over the course of this reaction.