What is referred to as the basic unit of matter consisting of protons, neutrons, and electrons?

The basic unit of matter, which includes protons, neutrons, and electrons, is best described as a chemical element. Each chemical element is defined by its unique number of protons in the nucleus, which determines the element's identity. The protons and neutrons form the nucleus at the center of an atom, while electrons orbit around this nucleus. This atomic structure is fundamental to understanding chemistry and the properties of matter.

The other options refer to different concepts. Atomic structure broadly describes how atoms are arranged and interact, while molecular structure specifically pertains to how atoms bond together to form molecules. Subatomic particles, while accurately naming protons, neutrons, and electrons, do not encompass the entire unit of matter as an atom. Thus, the term that most accurately captures the concept of the basic unit of matter in its entirety is chemical element.