Protective Oxide Layer Prevents Aluminium Corrosion

Steps:

• Recall that corrosion involves reaction with oxygen or water; aluminium is reactive but doesn't corrode quickly.
• Note aluminium's position in the reactivity series: above hydrogen, so it should displace hydrogen from acids but resists atmospheric corrosion.
• Identify the key factor: a thin, impermeable layer forms on the surface during initial exposure.
• Confirm the layer's composition: it's aluminium oxide (Al₂O₃), which adheres tightly and blocks further oxygen access.

Why D is correct:

• Aluminium reacts with oxygen to form Al₂O₃, a stable, passive layer that acts as a barrier, preventing further oxidation per the passivation principle in electrochemistry.

Why the others are wrong:

• A: Aluminium is above hydrogen in the reactivity series, making it more reactive, not less.
• B: Being above hydrogen explains reactivity potential but not slow corrosion; the oxide layer is the actual protector.
• C: No protective nitride layer forms; aluminium nitride (AlN) occurs in specific industrial processes, not natural corrosion.

Final answer: D