What element is added to stainless steel to enhance its corrosion resistance?

The correct choice is chromium, which is an essential element in the composition of stainless steel and plays a crucial role in enhancing its corrosion resistance. When chromium is added to steel, it reacts with oxygen to form a thin, passive layer of chromium oxide on the surface. This layer acts as a protective barrier, preventing oxygen and moisture from reaching the underlying steel and, therefore, inhibiting rust and corrosion.

While molybdenum is also used in some stainless steel grades to improve corrosion resistance, especially in more aggressive environments, chromium is the primary element responsible for the hallmark corrosion resistance of stainless steel. Nickel, another additive, can improve toughness and ductility but does not directly contribute to corrosion resistance in the same way that chromium does. Iron is the main component of steel but does not improve corrosion resistance on its own. Thus, chromium is recognized as a critical element for ensuring the durability and longevity of stainless steel in various applications.