Which of the following best describes an alloy?

An alloy is characterized as a mixture of two or more elements, with at least one of those elements being a metal. This definition encompasses a wide range of materials, such as steel (which is a mixture of iron and carbon) and bronze (a mixture of copper and tin). The properties of alloys often differ significantly from those of the individual metals used to create them; for example, they may exhibit improved strength, resistance to corrosion, or enhanced electrical conductivity.

In contrast, the other options do not accurately reflect the nature of alloys. A mixture of gases refers to a blend of different gaseous substances without any metallic component. A solution of salt in water describes a homogeneous mixture formed when salt dissolves in water, which does not involve metals in the typical sense of alloy composition. Additionally, a compound formed by a chemical reaction consists of substances that are chemically bonded together, rather than merely mixed, which is fundamentally different from how alloys function.