Final answer:
During glycolysis, a glucose molecule is split into two pyruvate molecules, with a net gain of two ATP molecules and production of two NADH molecules; therefore, the answer is 'All of the above'.
Step-by-step explanation:
When glycolysis occurs, a molecule of glucose is indeed split, two molecules of pyruvate are formed, and there is a production of ATP. Specifically, glycolysis is the metabolic pathway that converts glucose (C6), which is a six-carbon sugar, into two three-carbon molecules of pyruvate. At the start of glycolysis, two ATP molecules are used to energize the splitting of glucose. As the process continues, four ATP molecules are produced, resulting in a net gain of two ATP molecules for the cell. Additionally, a pair of energy-carrying molecules NADH are also formed during glycolysis. Therefore, the correct answer that encapsulates all aspects of the glycolysis stage is All of the above (1, 2, and 3).