Iron rusts because of ______ reaction.

Explanation:

Confusion Points

• During rusting, iron combines with oxygen in the presence of water. This is an oxidation reaction where oxygen acts as an oxidizing agent.
• Since oxygen also combines with the metal iron, this is a reduction reaction, where the metal iron acts as a reducing agent.
• So here both oxidation and reduction process is taking place. This combination of these processes is a redox reaction. So the correct answer is the redox reaction. 

Key Points

Rusting of iron is an example of a Redox reaction.

• Redox reaction = Oxidation-Reduction reaction. In this reaction, an oxidation number of a molecule, atom, or ion changes either by gaining or losing an electron. 
• The substance which gets reduced in a chemical reaction is known as the oxidizing agent and a substance that gets oxidized in a chemical reaction is known as the reducing agent.
• Rusting is the corrosion of iron. Iron forms red-brown hydrated metal oxide (rust) in the presence of water and air. 
• Iron is oxidized to Fe2+ and oxygen is reduced to water. Rust keeps on forming due to the subsequent oxidation of Fe2+ by atmospheric oxygen.
• Therefore, we can say rusting is a redox reaction because oxygen acts as an oxidising agent, and iron acts as a reducing agent.

Rusting of Iron takes place:

• Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.
• Fe + O2  → Fe2O3 (Iron (III)oxide)

Important Points

Oxidation and Reduction:

• Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. Iron and steel rust when they come into contact with water and oxygen – both are needed for rusting to occur.
• When acidic substances (including water) come in contact with metals, such as iron and/or steel, rust begins to form. Rust is the result of corroding steel after the iron (Fe) particles have been exposed to oxygen and moisture (e.g., humidity, vapor, immersion).
• The addition of oxygen to a substance and the removal of hydrogen from a substance is called oxidation.
• The addition of Hydrogen in a substance and the removal of oxygen from a substance is called reduction.