The right answer is 3. Glucose is broken down in glycolysis, yielding two ATP; after the Krebs cycle, NADH and FADH2 are formed, yielding NAD+ and FAD in ETS reactions.
In aerobic:
* Assessment of glycolysis: theoretical formation of 6 ATP (5 ATP actually).
* Assessment of the catabolism of pyruvate: formation of 3 ATP per molecule of pyruvate in theory (2.5 in reality) and therefore of 6 ATP in theory (5 ATP in reality) for a molecule of glucose.
* Review of the Krebs cycle: theoretically 12 ATP per molecule of acetyl coenzyme A (10 ATP in reality) and thus 24 ATP (20 ATP in reality) for one molecule of glucose.
The overall theoretical balance of the degradation of an aerobic glucose molecule is therefore 36 ATP (30 ATP actually) which are not immediately mobilizable because the majority of the ATP formed come from oxidative phosphorylation.
It is important to specify here that some works speak of a global theoretical balance of 38 ATP; this difference can be explained by the type of shuttle used
