Enzyme common to cholesterol synthesis and ketone body synthesis:

Enzymes common to cholesterol synthesis & ketone body synthesis are HMG CoA Synthase & Thiolase. HMG CoA Synthase (Option 2) is rate limiting step in Ketone Body synthesis. HMG CoA Reductase (Option 1) is rate limiting step in cholesterol synthesis. Beta hydroxy butyrate Dehydrogenase (Option 3) is only used in ketone body synthesis. Thiophorase (Option 4) is the first enzyme in ketone body utilization. First two steps of Cholesterol Synthesis are same as Ketone Body Synthesis but Cholesterol Synthesis occurs in Cytoplasm whereas Ketone Body Synthesis occurs in Mitochondria.