Here's why:

* Pyruvate Oxidation: Pyruvic acid (C3H4O3) is converted into acetyl-CoA (C2H3O3S-CoA), which enters the Krebs cycle. This process releases one molecule of carbon dioxide.

* Krebs Cycle: The Krebs cycle then further oxidizes the acetyl-CoA, resulting in the release of two more molecules of carbon dioxide.

Therefore, one molecule of pyruvate leads to the release of a total of three carbon dioxide molecules, but only one is released during the initial oxidation step.