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

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.

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.