How is a "substance" best defined in science?

In scientific terms, a "substance" is best defined as a type of matter that constitutes materials. This definition encapsulates the idea that substances are identifiable and uniform in chemical composition and properties, distinguishing them from mixtures, which consist of two or more different substances combined together.

Substances can be elements, like oxygen or gold, or compounds, like water or sodium chloride, and they exhibit consistent characteristics such as boiling point, melting point, and density. This understanding of a substance forms a fundamental concept in chemistry and material science, emphasizing the importance of purity and specific composition.

Other options describe different concepts: a mixture refers to combined materials that can vary in composition and can be separable, an electrical component that stores energy relates to devices like capacitors and batteries, and a biological organism pertains to living entities within ecosystems. Each of these serves a different context and purpose in their respective fields, but they do not align with the scientific definition of a substance.