Which of these is NOT an organic compound?

• A. CH4 (methane).
• B. C6H12O6 (glucose).
• C. CH3COOH (acetic acid).
• D. HCl (hydrochloric acid).

Answer: (D)

Understanding what makes a compound organic: organic compounds are built around carbon atoms, usually with hydrogen attached, forming carbon–hydrogen bonds and carbon skeletons. The molecules methane, glucose, and acetic acid all contain carbon and hydrogen (with additional oxygen in some), so they clearly fit into organic chemistry. Hydrochloric acid, on the other hand, is just hydrogen bonded to chlorine and contains no carbon at all, so it does not belong to the organic category.