Carbon monoxide (CO) is a colorless, odorless, and tasteless gas which is slightly lighter than air.
It is highly toxic to humans and animals in higher quantities, although it is also produced
in normal animal metabolism in low quantities, and is thought to have some normal biological functions.
Carbon monoxide consists of one carbon atom and one oxygen atom, connected by a triple bond which consists
of two covalent bonds as well as one dative covalent bond. It is the simplest oxide of carbon.
In coordination complexes the carbon monoxide ligand is called carbonyl.
Carbon monoxide is produced from the partial oxidation of carbon-containing compounds;
CO forms when there is not enough oxygen to produce carbon dioxide (CO2), such as when operating a stove
or an internal combustion engine in an enclosed space. This makes it a pollutant of concern primarily
for traffic, as well as indoor air pollution.
In the presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide, CO2.
Coal gas, which was widely used before the 1960s for domestic lighting, cooking and heating,
had carbon monoxide as a significant constituent.
Some processes in modern technology, such as iron smelting, still produce carbon monoxide as a byproduct.[