Redox cofactors — The ability of FADH (reduced flavin) to be oxidized is __________ compared with the ability of FAD (oxidized flavin) to be oxidized.

Introduction / Context:
Flavin adenine dinucleotide (FAD) participates in numerous dehydrogenase reactions. Its redox pairs, FAD/FADH2 (often written FAD/FADH or FADH2 depending on protonation state), cycle between oxidized and reduced forms. Understanding which form can undergo oxidation or reduction is key to tracking electron flow in metabolism.

Given Data / Assumptions:

• “Oxidized” means loss of electrons; “reduced” means gain of electrons.
• FAD is oxidized; FADH or FADH2 is reduced.
• We compare each form’s ability to be oxidized.

Concept / Approach:
Only the reduced form can be oxidized (it can donate electrons). The oxidized form (FAD) cannot be oxidized further; it can only accept electrons (be reduced). Therefore, the ability of FADH (reduced flavin) to be oxidized is greater than that of already-oxidized FAD. In electron transport, FADH2 donates electrons to the chain, demonstrating its readiness to be oxidized back to FAD.

Step-by-Step Solution:

Verification / Alternative check:
Succinate dehydrogenase (Complex II) transfers electrons from succinate to FAD, forming FADH2, which is then oxidized as it passes electrons to the ubiquinone pool, illustrating the oxidizability of the reduced flavin.

Why Other Options Are Wrong:

• Lesser/approximately equal/half: contradict the basic redox logic; an already oxidized cofactor cannot be oxidized further.

Common Pitfalls:
Confusing a molecule’s capacity to be oxidized with its role as an oxidizing agent. FAD (oxidized) is an oxidizing agent (accepts electrons), but its own ability to be further oxidized is nil.

Final Answer:
greater