What are alkenes?

• A. Hydrocarbons with double bonds
• B. Hydrocarbons with single bonds
• C. Aromatic hydrocarbons
• D. Hydrocarbons with triple bonds

Answer: (A)

Alkenes are hydrocarbons that contain a carbon–carbon double bond. That double bond makes the molecule unsaturated and enables addition reactions across the bond, which is a hallmark difference from single-bond hydrocarbons. The double bond also means the involved carbons are sp2-hybridized, giving a planar region around the bond and, when substituents are different, allowing geometric isomerism (cis/trans). For straight-chain alkenes, the general idea is CnH2n, reflecting the loss of two hydrogens compared with alkanes. They are distinct from alkanes (single bonds), aromatic hydrocarbons (ring systems with delocalized electrons), and alkynes (triple bonds). So the defining description is hydrocarbons with double bonds.