Which type of hydrocarbon has carbon atoms linked by double bonds?

The type of hydrocarbon characterized by carbon atoms linked by double bonds is alkenes. Alkenes are defined by the presence of at least one carbon-carbon double bond (C=C) in their structure, which is what sets them apart from other types of hydrocarbons.

In comparison, alkanes are saturated hydrocarbons and contain only single bonds between carbon atoms (C-C), making them relatively less reactive than alkenes. Alkynes, on the other hand, contain at least one carbon-carbon triple bond (C≡C), which differentiates them from alkenes since they have a different bonding structure. Arenes, also known as aromatic hydrocarbons, feature a ring structure with alternating single and double bonds, which gives them unique chemical properties, but they don't solely consist of double bonds like alkenes.

Thus, the defining characteristic of alkenes—having at least one double bond—makes them the correct choice in this context.