One molecule of FADH₂ is produced in the Krebs cycle during the conversion of:

Explanation

The conversion of succinate to fumarate is the correct step where one molecule of FADH₂ is produced in the Krebs cycle. This reaction is catalyzed by the enzyme succinate dehydrogenase, which is located on the inner mitochondrial membrane. During this oxidation process, two hydrogen atoms are removed from succinate and transferred to flavin adenine dinucleotide (FAD), reducing it to FADH₂. This reduced coenzyme later donates electrons to the electron transport chain, contributing to ATP production. The reason FAD rather than NAD⁺ is used here is that the oxidation of succinate is not sufficiently energetic to reduce NAD⁺, but it is enough to reduce FAD.The conversion of fumarate to malate involves the addition of water, not the reduction of FAD. The conversion of α-ketoglutarate to succinate produces NADH and CO₂, not FADH₂. The conversion of malate to oxaloacetate also produces NADH, not FADH₂.