Considering the definition of redox reactions, the correct answer is the last option: Oxygen is reduced, and iron is oxidized.
<h3>Oxidation and reduction</h3>
Oxidation is a reaction where an atom, ion or molecule loses electrons while reduction corresponds to the gain of electrons from an atom, ion or molecule.
<h3>Redox reactions</h3>
The oxidation and reduction reactions always occur simultaneously for what are generally known as oxidation-reduction reactions or redox reactions.
That is, a redox reaction is a chemical reaction that occurs between an oxidizing substance and a reducing substance. During the reaction, the oxidizing substance loses electrons and the reducing substance gains electrons.
<h3>Oxidizing and reducing agent</h3>
That is, the oxidizing agent is the one that traps the electrons while the reducing agent is the one that provides the electrons.
<h3>This case</h3>
In this case, when iron pipes come in contact with water and oxygen, iron transfers electrons to the oxygen molecules. So, iron loses electrons while oxygen gains electrons. So oxygen is reduced, and iron is oxidized.
Then, the correct answer is the last option: Oxygen is reduced, and iron is oxidized.
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