C2H6 is the answer Alkanes, alkenes and alkynes are simple hydrocarbon chains with no functional groups. Alkanes are identified because the carbon chain has only single bonds. Common alkanes include methane (natural gas), propane (heating and cooking fuel), butane (lighter fluid) and octane (automobile fuel). Alkenes have at least one double bond and alkynes have at least one triple bond. The most common alkyne is ethyne, better known as acetylene. The generic formula for alkanes is CnH2n+2, where n is the number identified by the prefix. Alkenes have the formula CnH2n and alkynes use the formula CnH2n-2