Which of the following materials is most susceptible to corrosion in a saltwater environment?

Carbon steel is the material most susceptible to corrosion in a saltwater environment due to its composition, which is primarily iron. When exposed to saltwater, the presence of chloride ions accelerates the electrochemical process of rusting. Chlorides invade the protective oxide layer that normally forms on iron, leading to rapid corrosive attacks and pitting.

In contrast, plastics are not conductive and are generally inert to saltwater, providing good resistance to corrosion. Stainless steel, while still vulnerable, typically contains alloying elements such as chromium, which enhance its corrosion resistance by forming a protective passive layer on its surface. Copper, though it can corrode, develops a protective patina that slows further corrosion in marine environments. Thus, carbon steel stands out as the most susceptible material to corrosion in this scenario, making it particularly important to take preventative measures when using it in marine applications.