Carbon molecules can have varying numbers of double bonds depending on the specific molecule and its structure. Alkenes, for example, are hydrocarbons that contain at least one carbon-carbon double bond. The number of double bonds in a carbon molecule can range from one to several, depending on the size and complexity of the molecule. For instance, ethene (C2H4) has one double bond, while butadiene (C4H6) has two double bonds. Additionally, some carbon molecules may have multiple double bonds, such as benzene (C6H6), which has three double bonds. The number of double bonds in a carbon molecule affects its chemical properties and reactivity.