Which of the following is not a hydrocarbon subgroup?

• A. Paraffins/alkanes
• B. Naphthenes/Cycloalkanes
• C. Aromatic compounds
• D. Alkenes

Answer: (D)

Hydrocarbons are compounds made only of carbon and hydrogen, and they fall into groups based on structure and bonding. Parafins (alkanes) are saturated open chains, naphthenes (cycloalkanes) are saturated rings, and aromatic compounds are ring systems with delocalized electrons. Alkenes are also hydrocarbons, defined by having at least one carbon–carbon double bond, so they belong to the hydrocarbon family as well. Because all four options describe hydrocarbon categories, there isn’t a true option that isn’t a hydrocarbon subgroup. If a choice must be made in some contexts, the question itself may be flawed since alkenes are indeed hydrocarbons.