What type of bond is characteristic of an alkene?

Alkenes are hydrocarbons that are characterized by the presence of at least one carbon-carbon double bond. This double bond consists of one sigma (σ) bond and one pi (π) bond, which allows for a specific type of reactivity and geometry that distinguishes alkenes from alkanes (which have only single bonds) and alkynes (which contain triple bonds).

The double bond in alkenes affects the physical and chemical properties of the molecule, such as its reactivity, boiling points, and isomerism. The presence of this double bond means that alkenes can participate in addition reactions, whereby other atoms or groups can be added across the double bond, leading to a variety of different products. This key feature makes the double bond characteristic of alkenes, thereby confirming that the correct answer is indeed the option representing a double bond.