Final answer:
FADH₂ becomes FAD+ through oxidation, not reduction. The process involves the loss of electrons as FADH₂ donates them to the electron transport chain during cellular respiration.
Step-by-step explanation:
When a molecule of FADH₂ becomes FAD+, it is not being reduced; rather, it is being oxidized. Reduction is the gain of electrons in a chemical reaction, which is not the case here. The process of FADH₂ becoming FAD+ involves the loss of two hydrogen atoms (2 H+ + 2 e⁻), which means FADH₂ is giving up electrons and protons during oxidative reactions, as seen in the electron transport chain. Thus, FAD is the oxidized form, while FADH₂ is the reduced form. This is significant in the context of cellular respiration where FADH₂, along with NADH, donate their electrons to the electron transport chain to help produce ATP, with FADH₂ transferring its electrons at complex II directly without passing through complex I like NADH.