An element is best described as a material consisting of only one type of atom. This means that all atoms in an element have the same number of protons in their nuclei, which defines the element’s identity. For example, gold is an element because it consists only of gold atoms.
Elements are the simplest forms of matter and cannot be broken down into simpler substances by chemical means. Each element has unique properties, such as atomic number, atomic mass, and chemical reactivity, which distinguish it from other elements.
Therefore, the correct answer is a. a material consisting of only one type of atom.