NADH and FADH are produced by the Citric Acid Cycle (CAC) and these electron shuttles go on to the Electron Transport Chain (ETC). If the ETC produce 51 moles of ATP from the products of the CAC, then how many moles of pyruvate entered the CAC

3 moles of Pyruvate entered CAC

Explanation:

2moles of pyruvate gives 34 ATP MOLES

Hence 51moles of ATP willl give 51*2/34, which is equal to 3moles

NADH is an energy carrier which delivers high energy electrons to the electron transport chain where they will eventually power the production of 2 to 3 ATP molecules.

FADH is another energy carrier that carries high energy electrons to the ETC, where they will drive the production of 1 to 2 ATP molecules.

Electron transport chain  produces most of the energy ( 34 ATP molecules, compared to only 2 ATP for glycolysis and 2 ATP for Krebs cycle). The electron transport chain takes place in the mitochondria. This stage converts the NADH into ATP.

NADH = 3ATP FADH2 = 2ATP