In glycolysis, the net gain is 2 ATP molecules and two molecules of:

Explanation

NADH is the correct product of glycolysis because it specifically involves the reduction of NAD+ to NADH when glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate. This step is catalysed by glyceraldehyde-3-phosphate dehydrogenase and is the only redox reaction in the glycolysis pathway. FADH₂ is not produced in glycolysis; it is generated later in the Krebs cycle when succinate is converted to fumarate. FMNH₂ is a form of flavin mononucleotide used in the electron transport chain, not in glycolysis, and NADPH is primarily produced in the pentose phosphate pathway for biosynthetic reactions, rather than in energy-yielding catabolism. Therefore, only NADH is formed in glycolysis as the electron carrier that will eventually donate electrons to the electron transport chain under aerobic conditions.