Final answer:
NADH has the most potential energy among the molecules NADH, NAD+, and FAD, as it can transfer more hydrogen ions across the mitochondrial membrane in the ETC, which contributes more significantly to the production of ATP.
Step-by-step explanation:
In the context of cellular respiration, the molecule with the most potential energy is NADH, compared to NAD+ or FAD. This is because NADH and FADH2 are high-energy molecules that play crucial roles in the electron transport chain (ETC) inside mitochondria. NADH enters the ETC at Complex I, while FADH2, the reduced form of FAD, enters at Complex II. NADH has enough potential energy to transport three hydrogen ions across the mitochondrial membrane, contributing to the creation of a proton gradient that drives ATP synthesis. In comparison, FADH2 has enough energy to transport only two hydrogen ions, making NADH the more energy-rich molecule of the two.