Final answer:
The two substances involved in the rusting of iron are oxygen and water, which cause iron to oxidize and form iron (III) oxide, or rust.
Step-by-step explanation:
The two types of substances involved in the rusting process of iron are oxygen and water. Iron undergoes a redox reaction where it is first oxidized to iron (II) ions (Fe2+) when it comes into contact with oxygen. This step occurs at anodic sites, which are often impurities or lattice defects on the iron's surface. Next, these iron (II) ions react with water and more oxygen to form a hydrated form of iron (III) oxide, commonly known as rust (Fe2O3·xH2O).
This process is not simply detrimental to the metal, but it also has significant economic implications, with corrosion estimated to cost the U.S. economy over $100 billion each year.