Which hydrocarbon type is characterized by having carbon-to-carbon double bonds?

The correct answer is characterized by the presence of carbon-to-carbon double bonds, which distinctly identifies it as having unsaturation in its structure. Alkenes comprise this type of hydrocarbon, where at least one double bond exists between two of the carbon atoms in the molecule. This double bond not only affects the physical and chemical properties of alkenes but also allows for reactions such as addition reactions, where other atoms can add across the double bond, further expanding their versatility in chemical reactions.

In contrast, alkenes differ from alkanes, which are saturated hydrocarbons and contain only single bonds between carbon atoms. Thus, while alkanes have the maximum number of hydrogen atoms that can bond to the carbon framework (making them saturated), alkenes do not, due to the presence of the double bond, making them unsaturated. Alkynes, on the other hand, are characterized by carbon-to-carbon triple bonds, which is another form of unsaturation and does not apply to this question. Saturated hydrocarbons refer generally to alkanes, reaffirming the distinction between them and alkenes.