Which by-product is created when ferrous oxide forms due to corrosion in pipes?

The correct by-product formed when ferrous oxide experiences corrosion in pipes is hydrogen sulfide. This process typically occurs in anaerobic conditions where sulfur-reducing bacteria are present, leading to the reduction of sulfates or organic sulfur compounds, resulting in hydrogen sulfide.

Understanding the formation of ferrous oxide during the corrosion process is crucial. Corrosion generally involves the oxidation of iron, which can generate a range of compounds, but in the context of sulfur presence and anaerobic conditions, it is particularly linked to the production of hydrogen sulfide.

The other by-products listed do not directly relate to the corrosion of ferrous oxide in this context. Sulfur oxide, for example, is associated with the combustion of sulfur-containing materials rather than the corrosion of iron. Carbon monoxide is a by-product of combustion processes involving carbon, and methane gas primarily results from anaerobic digestion and decomposition of organic matter rather than being directly linked to iron corrosion.