What chemical substance is abbreviated CO2?

The chemical substance abbreviated CO₂ is carbon dioxide.

A molecule of carbon dioxide contains one carbon atom covalently bonded to two oxygen atoms, which gives it the formula CO₂. At ordinary temperatures and pressures, it is a colorless gas and is usually odorless at low concentrations.

Carbon dioxide is released by respiration, combustion, decomposition, and volcanic activity. Plants, algae, and cyanobacteria absorb it during photosynthesis, using sunlight to make sugars and releasing oxygen. This makes CO₂ a central part of Earth’s carbon cycle.

A common mix-up is confusing carbon dioxide with carbon monoxide, CO. Carbon monoxide contains one oxygen atom, is highly poisonous, and is produced by incomplete combustion. Solid carbon dioxide is called dry ice; it changes directly from a solid to a gas rather than melting at normal atmospheric pressure.