Final answer:
The correct answer is that oxidative phosphorylation in the mitochondria produces most of the ATP and this occurs in the electron transport chain located on the inner mitochondrial membrane, not the citric acid cycle in the matrix.
Step-by-step explanation:
The stage inside the mitochondria that produces 28 molecules of ATP through oxidative phosphorylation is known as the electron transport chain. This process involves the transfer of electrons from NADH and FADH2 along a series of protein complexes embedded in the inner mitochondrial membrane. The electron flow drives protons across this membrane, creating a proton gradient that powers ATP synthase to produce ATP through a process called chemiosmosis.
The citric acid cycle, also known as the Krebs cycle, which takes place in the mitochondrial matrix, provides the electron carriers NADH and FADH2 used in the electron transport chain. Most of the ATP is produced in mitochondria by oxidative phosphorylation.