Which statement correctly contrasts ferrous and non-ferrous metals and mentions a typical corrosion issue for each class?

• A. Ferrous metals contain iron and rust in moist environments; non-ferrous metals do not contain iron and resist rust; aluminium forms a protective oxide and copper develops a patina that protects it.
• B. Non-ferrous metals contain iron and rust in moist environments.
• C. Ferrous metals include aluminium and copper.
• D. All metals contain iron and rust in moist environments.

Answer: (A)

Ferrous metals are defined by iron content, so they rust in moist environments because iron reacts with water and oxygen to form iron oxide. Non-ferrous metals do not contain iron, so they don’t rust in the same way. A typical corrosion behaviour for aluminium is that it rapidly forms a very thin, adherent oxide layer that passivates the surface and greatly reduces further corrosion. Copper develops a patina—a greenish layer of copper carbonate/oxide—that also protects the metal from further corrosion. This combination of ideas correctly contrasts the two classes and notes a typical corrosion issue for each. The other statements clash with basic facts: non-ferrous metals don’t contain iron and don’t rust like ferrous metals, aluminium and copper are non-ferrous, and not all metals contain iron.