Enzyme responsible for complete oxidation of glucose to CO2 and water is present in:: (A) Cytosol, (B) Mitochondria, (C) Lysosomes, (D) ER
Answer is B. Under aerobic conditions, pyruvate is taken up into mitochondria, and after oxidative decarboxylation to acetyl-CoA is oxidized to CO2 by the citric acid cycle.
Under anaerobic conditions, pyruvate is reduced by the NADH to lactate, catalyzed by lactate dehydrogenase.

(Ref: Harper Ed. 29th pg173, Ed 30th pg 172)