The answer is 10 NADH.
For each glucose molecule that enters glycolysis, a total of 10 NADH are produced.
That is; during glycolysis 2 NADH are produced, while another two are produced in the conversion of pyruvic acid to acetyl-CoA, and in the Citric acid Cycle 6 NADH are produced, that makes a total of 10 NADH, which are then taken to the electron transport chain to produce ATP.