The corrosion product known as iron oxide is commonly called what?

• A. Iron rust
• B. Copper patina
• C. Aluminum hydroxide
• D. Magnesium oxide

Answer: (A)

Rust is the common name for the corrosion product of iron. When iron or steel is exposed to moisture and oxygen, it oxidizes to iron oxide, often forming hydrated forms like Fe2O3·nH2O or FeOOH. This coating, called rust, is typically reddish-brown, flaky, and porous, offering little protection and allowing continued corrosion. The other options refer to corrosion products of different metals or to compounds not formed from iron in ordinary conditions, so they don’t apply.