Is CO₂ acidic or basic?

Answer: Carbon dioxide (CO₂) is regarded as an acid or a Lewis acid because of resonance, which causes it to act as a Lewis acid (which accepts a lone pair of electrons). The gas carbon dioxide, or CO₂, has no smell. Typically, it is referred to as an “odorless” gas. The atmosphere of the Earth is constantly filled with non-toxic carbon dioxide.

When CO₂ is dissolved in water, carbonic acid is created:

CO₂(g)+H₂O(l)⇌H₂CO₃(aq)