Which of the following pipes is most susceptible to corrosion?

The pipe material that is most susceptible to corrosion is iron or steel. This vulnerability is primarily due to the fact that iron and steel are ferrous metals, which means they contain iron as a primary component. When exposed to moisture and oxygen, ferrous metals undergo a chemical reaction that leads to rust formation, compromising the integrity of the pipe over time. Common environments that exacerbate this issue include areas with high humidity, aggressive soil conditions, and instances where water quality has high levels of corrosive elements.

In contrast, copper is generally more resistant to corrosion, especially when not exposed to acidic conditions. PVC, being a plastic, does not corrode in the same way and is resistant to most chemicals; therefore, it offers better long-term durability against corrosion. Cast iron also has a certain level of corrosion resistance when properly coated or maintained, but it can still suffer from rust under certain conditions. However, iron and steel, without proper protective measures, experience significantly higher rates of corrosion, making them the most susceptible among the choices provided.