(d) : The last step of aerobic respiration is the oxidation of reduced coenzymes, i.e., NADH2 and FADH ‌2 by molecular oxygen through FAD, ubiquinone, Cytb,Cytc,Cytc1,Cyta and Cyta3 By oxidation of 1 molecule of NADH2,3 ATP molecules are produced and by oxidation of 1 molecule of FADH 2,2 ATP molecules are produced. In glycolysis 2 ATP molecules are produced from ADP. Further 2NADH2 produced, give 2×3=6 ATP, on oxidative phosphorylation. Similarly in Krebs' cycle 2 ATP molecules are produced. So the greatest number of ATP molecules are produced in the electron transport chain.