Final answer:
Iron oxidizing bacteria produce iron oxide as a byproduct of their metabolic process, which involves the oxidation of ferrous ions (Fe2+) to ferric ions (Fe3+).
Step-by-step explanation:
Iron oxidizing bacteria are known to produce iron oxide as a byproduct of their metabolic processes. These bacteria oxidize ferrous ions (Fe2+) to ferric ions (Fe3+), resulting in the formation of iron oxide compounds, most commonly rust (Fe2O3 or Fe3O4). These reactions are part of their energy-producing pathway, wherein iron serves as an electron donor, and oxygen usually acts as the final electron acceptor.
When considering the reactions presented:
When hydrogen gas is passed over heated iron oxide, iron and steam are produced, signifying a redox reaction where iron oxide is being reduced to iron. In the presence of iron and oxygen, however, iron oxidizing bacteria will conversely contribute to the oxidation of iron, leading to the production of iron oxide.