What is formed by the chemical reaction of oxidation in pipes, commonly known as rust?

The formation of rust in pipes occurs through the oxidation process, specifically involving iron and oxygen in the presence of moisture. When iron reacts with oxygen, particularly when there is water present, it leads to the development of ferrous oxide, commonly referred to as rust. This compound is typically characterized by its reddish-brown color and can significantly weaken the structural integrity of metal pipes over time if not addressed.

In contrast, the other chemical compounds listed arise from different chemical reactions that do not relate to the oxidation of iron. Carbon dioxide is produced through organic matter decomposition and respiration, while methane gas results from anaerobic digestion processes, and sulfur oxide is a product of the combustion of sulfur-containing materials. Therefore, the understanding of rust formation directly points to ferrous oxide as the correct answer. This knowledge is essential for maintaining the durability and functionality of plumbing systems, ensuring they remain free from corrosion and other detrimental effects caused by rust.