Final answer:
Rust is produced when iron reacts with water and oxygen. In some cases, impurities on the iron surface can cause the production of something else along with rust.
Step-by-step explanation:
Rust is the result of the corrosion of metallic iron, and it is a chemical process that occurs when iron is exposed to water and oxygen. When iron corrodes, it forms a red-brown hydrated metal oxide called rust. Rust continually flakes off, exposing a fresh metal surface vulnerable to reaction with oxygen and water.
However, in some cases, something else can be produced along with rust. For example, in the presence of impurities or lattice defects on the iron surface, iron can be oxidized to Fe2+(aq), and oxygen can be reduced to water. This reaction occurs at different sites on the iron surface, acting as the anode and cathode, respectively. Electrons are transferred from the anode to the cathode through the electrically conductive metal, and the rust (Fe2O3∙xH2O) is formed by the subsequent oxidation of Fe2+ by atmospheric oxygen.