What is a compound?

A compound is defined as a pure substance that is formed when two or more different elements chemically combine in a fixed ratio. The resulting substance has unique properties that are distinct from the properties of the individual elements that composed it. For example, water (H₂O) is a compound made from hydrogen and oxygen. The chemical bonding between the elements gives the compound its characteristic behavior and features, which differ from those of hydrogen or oxygen on their own.

The other options do not accurately describe what a compound is. A type of element would refer to a single kind of atom, while a pure substance made from one atom misrepresents compounds, as they must consist of more than one type of element. Finally, an uncharged particle does not encompass the concept of a compound, which involves specific chemical combinations and interactions between elements. Thus, the description provided in the correct answer captures the essential characteristics of a compound accurately.