Which of the following metals is considered passive?

The correct answer identifies gold as the metal considered passive. A passive metal is one that exhibits little to no reactivity under certain conditions, often because it forms a protective oxide layer that prevents further oxidation.

Gold, being highly stable and resistant to corrosion, does not readily react with other substances, including acids. This characteristic stems from its noble nature, which results from its electron configuration. Unlike other metals, gold doesn't easily lose electrons to form cations, thereby maintaining its integrity in various environments.

In comparison, while copper and lead can display some level of resistance to corrosion due to the formation of surface oxides, they are not as inert or passive as gold. Iron, on the other hand, is quite reactive, especially with oxygen and moisture, leading to rust formation under typical conditions. The stability of gold makes it a near-ideal candidate for applications requiring durability and minimal reactivity, reinforcing its classification as a passive metal.