Reduction potential refers to the spontaneity of the reduction half reaction. Remember that reduction refers to a gain of electrons. Thus, reduction potential is similar to the property of electronegativity. It can also be thought of a molecule's tendency to gain electrons or as a measure of its unwillingness to give up electrons.

Since oxygen is the final electron acceptor in the electron transport chain, we know that the reduction of oxygen is highly spontaneous (highly positive E, and highly negative G). It is this reason that the electrons from NADH and FADH₂ must be passed step-wise to oxygen. Otherwise, there is such a large release of energy that too much would be lost to heat and become unavailable to do work for the cell.

In this question, we're asked to determine which scenario would cause a reduction in the amount of  produced by mitochondria.

First, let's start with  and . Both of these cofactors serve as high-energy electron carriers, which donate their electrons into the mitochondrial electron transport chain to ultimately produce . Therefore, high levels of these cofactors would not be expected to reduce  production.

Next, let's consider the effect of a higher pH in the matrix than in the intermembrane space. When the above mentioned cofactors donate their electrons into the electron transport chain, protons are actively pumped from the matrix into the intermembrane space. The result of this is that the intermembrane space becomes significantly more acidic than the matrix. This is needed, because the protons are then able to spontaneously flow down their proton gradient to produce . Therefore, we would expect that a higher pH (more basic) in the matrix is the equivalent to saying that the intermembrane space has a lower pH (more acidic). Consequently, this lower pH in the intermembrane space would be expected to produce  rather than inhibit its production.

Finally, lets consider how the concentration of  affects  production. In order to produce  via the electron transport chain,  needs to be phosphorylated. Therefore, if there is not much  around to phosphorylate, then we would expect that most of the cell's adenosine is already in the form of . Thus, we would expect low  concentrations to reduce  production.

The combustion of glucose to yield carbon dioxide and water refers to aerobic metabolism (oxidative phosphorylation). This process releases energy, so Gibbs free energy is negative. A negative Gibbs free energy indicates that the products are at a lower energy than the reactants, meaning that the reaction is thermodynamically favorable (spontaneous). Lastly, aerobic metabolism is called so because it requires oxygen. Thus, all of the answers are correct.

The complexes that function as a part of the electron transport chain accept electrons from  and .  When they accept the high energy electrons, they also pump hydrogens across the mitochondrial inner membrane to ultimately be used at the ATP synthase.  Creation of ATP is the end goal, but it is not made directly by the electron transport chain complexes.

Oxygen is required for the electron transport chain to function because it is the final electron acceptor for oxidative respiration. Once the high energy electron carriers,  and , have delivered electrons to the chain, the electrons run through the protein complexes. When they finish moving through all of the complexes, something must be available for them to attach to. Oxygen is the molecule responsible for this. It accepts the electrons and in turn is converted into .