Gold, represented by the chemical symbol Au, is classified as a pure substance. A pure substance is a form of matter that has a constant composition and properties that are constant throughout the sample. Gold is an element, which means it is made up of only one type of atom. Elements are the simplest form of matter and cannot be broken down into simpler substances by chemical means.
Gold is found in nature in its pure form, often as nuggets or grains in rocks, in veins, and in alluvial deposits. It is not mixed with other elements or compounds in its natural state, which further confirms its classification as a pure substance. The purity of gold is often measured in karats, with 24-karat gold being the purest form.
In summary, gold is a pure substance because it consists of only one type of atom and has a consistent composition and properties throughout.