Final answer:
The step in ethanol metabolism that happens in the mitochondria is Oxidation, where acetaldehyde is converted to acetate.
Step-by-step explanation:
The step in ethanol (ETOH) metabolism that occurs in the mitochondria is B. Oxidation. In the liver, ethanol is initially oxidized to acetaldehyde by the enzyme alcohol dehydrogenase in the cytoplasm. This oxidation reaction transforms the alcohol (OH) group of ethanol to a carbonyl (C=O) group in acetaldehyde. The acetaldehyde is then further oxidized in the mitochondria to acetate by the enzyme acetaldehyde dehydrogenase, which also involves the reduction of NAD+ to NADH. This process highlights the importance of enzyme-controlled oxidation reactions in providing the energy cells need to do useful work.