In glycolysis, the primary processes that occur are oxidation and substrate-level phosphorylation.
Specifically, oxidation occurs during the conversion of glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate, where NAD+ is reduced to NADH, indicating an oxidation reaction.
Hydrogenation and fixation do not occur in glycolysis. Hydrogenation typically involves the addition of hydrogen to a molecule, which is not a feature of glycolysis, while fixation refers to processes such as carbon fixation in the Calvin cycle, which is also not part of glycolysis.
So, among the given options, oxidation is the correct answer.