Which suffix indicates two carbon–carbon double bonds?

• A. An
• B. En
• C. Diene
• D. Yne

Answer: (C)

In naming hydrocarbons, the ending you attach to the root tells you about the number of carbon–carbon multiple bonds. A single double bond is indicated by the ending -ene. When there are two double bonds, the ending becomes -diene, with the di- prefix meaning two and the -ene part signaling double bonds. That’s why this option is the best choice for two C=C bonds, as seen in compounds like butadiene. The other endings don’t convey two double bonds: An isn’t a standard ending on its own, En isn’t used by itself (the correct form for a single double bond is -ene), and Yne denotes a triple bond, not double bonds.