Which of the options is a product of both the Krebs cycle and the electron transport chain?

ATP is the correct choice as it is a product of both the Krebs cycle and the electron transport chain. During the Krebs cycle, which occurs in the mitochondrial matrix, one molecule of ATP (or GTP, which can be readily converted to ATP) is produced for each turn of the cycle. This cycle is crucial for cellular respiration as it processes acetyl-CoA and generates electron carriers.

In addition, ATP production occurs in the electron transport chain (ETC) through oxidative phosphorylation. As electrons from NADH and FADH2 (produced in the Krebs cycle) are transferred along the chain, they release energy, which is used to pump protons across the mitochondrial inner membrane. This generates a proton gradient that results in the synthesis of ATP via ATP synthase when protons flow back into the mitochondrial matrix.

While FADH2 and NADH are indeed critical products of the Krebs cycle that feed into the electron transport chain, they themselves are not directly synthesized during the ETC. CO2 is a byproduct of the Krebs cycle, released during the decarboxylation processes, but it is not involved in ATP generation. Therefore, ATP stands out as the common product of both metabolic pathways.