Acetyl-CoA is formed when two carbon atoms join to coenzyme A. Ribose is a five carbon sugar in RNA. ATP is an energy compound, and FAD is an electron carrier in the Krebs cycle which gets reduced then passes its electron to an enzyme complex in the electron transport chain.

Carbon dioxide is the gas produced in the Krebs cycle, which animals exhale. Oxygen is used as an electron acceptor, while nitrogen is not a waste gas. Carbon monoxide is not a waste product in the Krebs cycle. 

The Krebs cycle involves aerobic respiration because oxygen is used. Anaerobic respiration involves fermentation because oxygen is lacking and the compound does not enter the Krebs cycle. Glycolysis is the first step in respiration, which precedes the Krebs cycle and is fully anaerobic. Note that oxygen is not directly required for the Krebs cycle (it is not a reactant), however, without oxygen, the electron transport chain will not proceed and thus the Krebs cycle will also be halted.

The two main products that result from the breakdown of glucose are carbon dioxide and water. Carbon dioxide is produced during pyruvate dehydrogenase and the Krebs cycle. Water is formed at the end of the electron transport chain where two electrons (hydrogens) are added to oxygen (the final electron acceptor).

Glycolysis generates four ATP per molecule of glucose and uses up two of those in the process, while oxidative phosphorylation produces thirty-two ATP per molecule of glucose. Fermentation produces NAD⁺, which is used in glycolysis. The citric acid cycle produces NADH and FADH₂, which are used in the electric transport chain. Note that for each turn of the citric acid cycle, three NADH molecules and one FADH₂ molecule is produced, but each glucose produces two pyruvate molecules, which are converted to two acetyl-CoA molecules. Each acetyl-CoA molecule results in one full turn of the citric acid cycle. The electron transport chain produces an electrochemical gradient across the inner membrane of the mitochondria, which provides the energy used by oxidative phosphorylation to produce thirty-two ATP per molecule of glucose.

The answer to this question is  is reduced.

 is least likely to occur because it is already in its reduced form. In actuality, it gets oxidized, as pyruvate is reduced into lactic acid. These other events are likely to occur. Your body does lack oxygen and lactate and ATP are produced in order to make up for the debt of oxygen.  also is recycled to be used in glycolysis so this event is also not least likely to occur.

The correct answer to this question is citrate.

Citrate is created when oxaloacetate reacts with acetyl-CoA and then citrate is converted to isocitrate, which then donates electrons and a hydrogen to . Malate is not involved in this process but it is an intermediate of the citric acid cycle. Glycinate is just a mineral supplement, and nitrate and oxalate have no role in the citric acid cycle.

This is because during glycolysis, a glucose molecule produces 2 ATP, 2 NADH, and 2 pyruvate. The 2 pyruvate created are used again to create 8 NADH, 2 FADH2, and 2 ATP during the Krebs cycle to net 10 NADH, 4 ATP, 2 FADH2.

In cellular respiration, oxygen is the final electron acceptor. Oxygen accepts the electrons after they have passed through the electron transport chain and ATPase, the enzyme responsible for creating high-energy ATP molecules. Just remember cellular respiration—respiration means breathing, and you cannot breathe without oxygen.

Oxygen is the final electron acceptor in the electron transport chain, showing the need for aerobic conditions to undergo such a process. ATP is produced as a product of the electron transport chain, while glucose and CO₂ play a role in earlier processes of cellular respiration.