What forms on all metals when they are exposed to the atmosphere?

When metals are exposed to the atmosphere, they naturally react with various elements, particularly oxygen. This reaction leads to the formation of a layer of metal oxides on the surface of the metal. The term "oxide" refers specifically to compounds that form when oxygen reacts with the metal. This oxide layer can serve as a protective barrier, although its effectiveness can vary between different metals.

For instance, aluminum forms aluminum oxide, which adheres well to its surface and protects the underlying metal from further oxidation. Similarly, iron can form iron oxide, commonly known as rust, which can be detrimental to structural integrity if not managed. The formation of oxides is a general process applicable to all metals but can differ in appearance and impact depending on the metal in question.

Options that mention corrosion, electrolysis, and patina refer to specific phenomena. Corrosion is a broader term describing the deterioration of materials, often as a result of the electrochemical reactions in the presence of moisture and other environmental factors. Electrolysis involves the movement of ions in a solution under an electric current, unrelated to the natural oxidation of metals. Patina refers to a specific green or brown film that forms on the surface of copper and bronze over time, which is caused by a combination of oxidation