The fundamental attribute of matter is its composition, which refers to the elements and particles that make up a substance. Matter is composed of atoms, which are the smallest units of matter that retain the properties of an element. Atoms themselves are made up of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus of the atom, while electrons orbit around the nucleus. The number of protons in an atom determines its atomic number and, consequently, its chemical properties. The arrangement and interaction of these particles within the atom define the physical and chemical behavior of matter.

The composition of matter is crucial because it dictates the substance's properties and its interactions with other substances. For instance, the number of electrons in an atom's outer shell influences its reactivity. Elements with a full outer shell are generally stable and unreactive, while those with incomplete outer shells are more reactive. This reactivity is the basis for chemical reactions, which involve the rearrangement of atoms and the formation of new substances.

Data from various scientific studies support the concept of composition as the fundamental attribute of matter. For example, the periodic table of elements, which organizes elements based on their atomic number and chemical properties, is a testament to the significance of atomic composition. Additionally, the study of isotopes, which are atoms of the same element with different numbers of neutrons, highlights the role of atomic composition in determining an element's mass and stability. The discovery of subatomic particles, such as quarks and leptons, further underscores the complexity of matter's composition and its role in shaping the universe.