Which of the following best describes an element?

An element is defined as a pure substance that consists entirely of one type of atom. This means that all atoms in an element have the same number of protons, which determines the atomic number and the properties of that element. For example, all carbon atoms have six protons, making them distinctly carbon, regardless of the amount or form in which they occur. Elements cannot be broken down into simpler substances by chemical means, which underscores their fundamental nature in chemistry.

In contrast to an element, a substance made of two or more types of atoms is classified as a compound or a mixture. Compounds involve chemical combinations of different elements, while mixtures can contain combinations of elements and/or compounds but do not have a chemical bonding. Similarly, substances that can be broken down into simpler substances often refer to compounds rather than elements. Therefore, the correct characterization of an element emphasizes its purity and homogeneity as consisting of only one type of atom.