Yes, carbon monoxide (CO) is considered a pure substance. A pure substance is defined as a material that has a uniform and definite composition. In the case of carbon monoxide, it is composed of one carbon atom and one oxygen atom, giving it a consistent molecular structure.
Carbon monoxide exists in the gas phase at room temperature and pressure, and its properties are uniform throughout. Unlike mixtures, which can vary in composition and properties, carbon monoxide maintains the same characteristics regardless of the source or method of production.
In summary, because carbon monoxide has a well-defined chemical composition and consistent properties, it is classified as a pure substance.