Final answer:
Carbon dioxide is not produced in the second stage of glycolysis; it is produced during the decarboxylation of pyruvate and in the Krebs cycle.
Step-by-step explanation:
The product not formed during the second stage of glycolysis is carbon dioxide (CO2). Glycolysis, occurring in the cytoplasm, consists of an energy investment phase followed by an energy generation phase. The second stage of glycolysis, also known as the energy payoff phase, results in the formation of ATP, NADH, and pyruvate. Carbon dioxide is not a product of this phase of glycolysis; instead, it is released during the oxidative decarboxylation of pyruvate and during the Krebs cycle.