Here's a breakdown:

* Hydrocarbon: A compound made up of only hydrogen and carbon atoms.

* Double bond: A chemical bond between two carbon atoms where they share two pairs of electrons.

The general formula for alkenes is C_nH_2n, where 'n' represents the number of carbon atoms.

Examples of alkenes:

* Ethene (C₂H₄): The simplest alkene, also known as ethylene.

* Propene (C₃H₆): An alkene with three carbon atoms.

* Butene (C₄H₈): An alkene with four carbon atoms.

Alkenes are important in many industries, including plastics, fuels, and pharmaceuticals.