Which one of the following respiratory reactions does NOT yield...

In the conversion of pyruvic acid to acetyl CoA (link reaction), oxidative decarboxylation takes place, releasing $\text{CO}_2$.

In alcoholic fermentation, pyruvic acid is first converted to acetaldehyde, releasing $\text{CO}_2$, which is then reduced to ethanol. Thus, the overall conversion of pyruvic acid to ethanol also yields $\text{CO}_2$.

In lactic acid fermentation, pyruvic acid (a 3-carbon compound) is directly reduced to lactic acid (also a 3-carbon compound) by the enzyme lactate dehydrogenase. Since there is no loss of carbon atoms, no decarboxylation occurs and no $\text{CO}_2$ is produced.

Answer: Pyruvic acid → Lactic acid