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 emphasizes that substances are made up of a specific arrangement of atoms and molecules, giving them distinct physical and chemical properties. For instance, substances can be elements, like gold or oxygen, or compounds, like water or sodium chloride.

This definition is central to the study of chemistry and material science, as it helps to distinguish pure materials from mixtures, which consist of two or more substances combined but not chemically bonded. Understanding a substance's identity and properties is crucial in fields such as chemistry, biology, and physics, where the interactions and behaviors of matter are analyzed and applied.

The other mentioned choices do not accurately capture the essence of what constitutes a substance in science. Mixtures do not represent a single type of matter, while electrical components and biological organisms pertain to specific categories within physics and biology, respectively, but do not define the broader concept of a substance.