Aluminium's Protective Oxide Layer

Steps:

• Observe that aluminium appears unreactive despite being a reactive metal.
• Recall that fresh aluminium reacts with oxygen to form aluminium oxide.
• Note that this oxide forms a thin, impermeable layer on the surface.
• Conclude the layer shields the metal underneath from further reactions.

Why A is correct:

• The oxide layer is a passive film that adheres tightly to the surface, preventing oxygen and other reactants from reaching the aluminium, as per the principle of passivation in corrosion science.

Why the others are wrong:

• B: Electrical conductivity relates to electron flow, not chemical reactivity.
• C: Low density affects weight and suitability for lightweight items, not reactivity.
• D: Group III position indicates electron configuration for bonding, but doesn't explain surface unreactivity.

Final answer: A