A glucose molecule is completely broken down in glycolysis and the Krebs cycle, but these two processes yield only a few ATPs. Where is the rest of the energy that the cell obtains from the glucose molecule? in the oxygen used in the electron transport chain in the carbon dioxide molecules released by the processes lost as heat in NADH and FADH2 in FAD and NAD

Cellular respiration process is organized into four stages: glycolysis, oxidative carboxylation, Krebs cycle and electron transport chain. These stages produce energy by saving in the bonds of ATP molecules and reducing equivalents called NADH and FADH₂.

Glycolysis produces 2 ATP from substrate-level phosphorylation and 2 NADH. Oxidative carboxylation or link reaction produces 2 NADH and Citric acid cycle produces 2 ATP and 6 NADH AND 2 FADH₂.

These stages produce energy by saving energy in the bonds of ATP molecules and NADH and FADH₂ as each NADH during electron transport chain produces 3 ATP and each FADH₂ produces 2 ATP.

Thus, in NADH and FADH₂ is the correct option.