The correct answer is option 1: oxygen forms a protective oxide layer.

Aluminium is more reactive than iron because it is higher up in the reactivity series of metals. This means that it is more likely to undergo chemical reactions with other substances. However, despite being more reactive, aluminium is less easily corroded than iron.

The reason for this is that when exposed to oxygen, aluminium forms a thin oxide layer on its surface. This oxide layer acts as a protective barrier, preventing further corrosion of the metal. It is stable and does not easily react with moisture or other substances in the environment. This is why aluminium is commonly used in structures and products that require resistance to corrosion, such as window frames, aircraft bodies, and food packaging.

Option 2, stating that aluminium is a noble metal, is incorrect. Noble metals, such as gold and platinum, are resistant to corrosion due to their low reactivity. Aluminium, on the other hand, is not classified as a noble metal.

Option 3, stating that iron undergoes reaction easily with water, is partially correct. Iron does react with water to form iron(II) hydroxide and hydrogen gas. However, this reaction does not directly explain why aluminium is less easily corroded than iron.

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