Which of the following is generated during one turn of the Citric Acid Cycle and can be used for energy?

FADH2 is generated during one turn of the Citric Acid Cycle when succinate is oxidized to fumarate. This process involves the enzyme succinate dehydrogenase, which transfers electrons to FAD, reducing it to FADH2. FADH2 is crucial because it acts as an electron carrier that enters the electron transport chain, where it is used to generate ATP, the primary energy currency of the cell.

In contrast, NAD+ is an electron carrier that is reduced to NADH during the cycle, but it is not the product that directly provides energy; rather, it is the reduced form (NADH) that plays a role in energy production. Oxaloacetate is a reactant that is regenerated at the end of the cycle, while citrate is an intermediate that is formed early in the cycle. Neither oxaloacetate nor citrate is directly usable for energy like FADH2. Thus, FADH2 represents the correct choice as it is directly involved in energy production through the electron transport chain.