How is an "alloy" defined?

An "alloy" is defined as a mixture of metals or a mixture of a metal and another element. This definition captures the essence of what alloys are in metallurgy. Alloys are created to enhance certain properties of the metals involved, such as strength, durability, corrosion resistance, and thermal conductivity.

For example, bronze is an alloy made primarily of copper and tin, which demonstrates improved hardness and resistance compared to pure copper. Alloys allow for the combination of different elemental properties to create materials that can be tailored for specific applications.

In contrast to the other options, a single metal in pure form does not meet the criteria for an alloy, as alloys involve the combination of multiple elements. Additionally, a compound formed between a metal and a gas does not describe an alloy since it highlights a chemical bond rather than a physical mixture. Lastly, a chemical reaction between metals does not define an alloy, as alloys are typically formed through the melting and mixing of metals rather than a reaction that produces a new substance.