The citric acid cycle (also known as the Krebs cycle or tricarboxylic acid (TCA) cycle) is a series of chemical reactions that occur in the mitochondria of cells to generate energy. During one complete turn of the citric acid cycle, two molecules of reduced nicotinamide adenine dinucleotide (NADH) and two molecules of reduced flavin adenine dinucleotide (FADH2) are produced.

Therefore, after four turns of the citric acid cycle, a total of 8 NADH and 8 FADH2 molecules would be produced.