What material is least likely to undergo rusting?

Copper is least likely to undergo rusting because rusting specifically refers to the corrosion process that affects iron and its alloys, such as steel. Rust forms when iron reacts with oxygen and moisture in the environment, resulting in iron oxide.

Copper, on the other hand, does not rust; it can slowly oxidize but forms a protective green patina (copper carbonate) that prevents further corrosion. This characteristic makes copper much more resistant to deterioration compared to iron and steel, which will continue to rust if exposed to the right conditions.

Aluminum is also resistant to corrosion, as it forms a protective layer of aluminum oxide when exposed to air, but it can still be affected under certain conditions. Thus, while iron and steel are highly susceptible to rusting, copper stands out as a material that is not prone to this specific form of corrosion.