The correct answer is that none of the citric acid cycle steps listed result in the production of . The only step of the citric acid cycle that results in the production of  is the conversion of succinate to fumarate (catalyzed by succinate dehydrogenase). In this reaction,  is concomitantly converted to  using the hydrogen molecules removed from succinate by succinate dehydrogenase. This reaction was not listed in the answer choices though, and therefore none of the reactions listed produced .

Each of the reactions listed did produce other side products. The conversions of isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate all result in the production of  as a side product, but not . The conversion of succinyl-CoA to succinate results in the production of ATP or GTP and CoA-SH as side products, but not . 

Flavin mononucleotide (FMN) is not produced by the citric acid cycle. This flavin coenzyme is a reactant, but not a product, since FMN will get reduced to FMNH₂.

The rest of the answer choices are products of the citric acid cycle (otherwise known as the Krebs cycle). 

Pyruvate is the end product of glycolysis. After glycolysis, the three-carbon molecule pyruvate is converted into the two-carbon molecule acetyl-coenzyme A (acetyl-CoA). This is carried out by a combination of three enzymes collectively known as the pyruvate dehydrogenase complex. The conversion of pyruvate to acetyl-CoA also produces one molecule of . Acetyl-CoA has one less carbon than pyruvate. The third carbon from pyruvate is lost as carbon dioxide () during the conversion of pyruvate to acetyl-CoA. Recall that since glucose is a six-carbon molecule, two molecules of pyruvate (three carbons each) are formed via glycolysis.

Pyruvate is produced in the last step of glycolysis, then, it is converted to the two-carbon molecule acetyl-coenzyme A (acetyl-CoA). This is carried out by a combination of three enzymes collectively known as the pyruvate dehydrogenase complex. The conversion of pyruvate to acetyl-CoA produces one . Acetyl-CoA has one less carbon than pyruvate. The third carbon of pyruvate is lost as carbon dioxide () during the conversion of pyruvate to acetyl-CoA. The citric acid cycle begins when the four-carbon molecule, oxaloacetate combines with acetyl-CoA (a two carbon molecule) via an aldol condensation, yielding the six-carbon molecule citrate.

During the conversion of succinate into fumarate by succinate dehydrogenase, a single molecule of  is reduced to  as it accepts the hydrogens from succinate.  then feeds its electrons into the electron transport chain in the inner mitochondrial membrane.

Succinyl-CoA synthetase performs substrate level phosphorylation at this step in the Krebs cycle, such that .

The conversion of pyruvate to acetyl-CoA produces one molecule of NADH, but remember that each glucose yields two pyruvates, so the total NADH from this first step is two. Within the citric acid cycle, there are three steps in which NADH is a byproduct, but again we must remember that each step occurs to two molecules, therefore three NADH byproducts for two molecules yields six NADH in the cycle proper. Therefore, the total NADH produced in one turn of the citric acid cycle is eight NADH. 

Citric acid cycle inputs are derived from glycolysis outputs. Glycolysis produces pyruvate molecules, , and ATP. The pyruvate molecules undergo reactions that convert the three carbon pyruvate to a two carbon acetyl CoA and an one carbon carbon dioxide. The acetyl-CoA molecules are then used as the initial inputs for the citric acid cycle, as they are combined with oxaloacetate. Note that pyruvate itself does not enter the citric acid cycle.  and are electron carriers that are produced in the citric acid cycle and are used in electron transport chain to generate ATP.

A glucose (six carbons) molecule enters glycolysis and produces two three carbon molecules (pyruvate). Each pyruvate is broken down into a two carbon acetyl-CoA molecule that enters the citric acid cycle. Each acetyl-CoA molecule produces three  and one  in the citric acid cycle. This means that two acetyl-CoA (derived from one glucose molecule) produces six  and two  molecules in the citric acid cycle.

Citric acid cycle involves a series of reactions that are involved in the production of the necessary molecules for electron transport chain. The cycle starts with a two carbon molecule (acetyl-CoA) binding to a four carbon molecule (oxaloacetate). This creates a six carbon molecule (citrate) that can go through a series of reactions. Most of these reactions involve a six carbon molecule. As mentioned, acetyl-CoA has two carbons; therefore, most of the intermediates in this cycle have six carbons, or four more carbons than acetyl-CoA. One turn of citric acid cycle produces , ,  (carbon dioxide) and one GTP molecule(s).