Which of the following is an example of a cyclic alkene?

Cyclic alkenes are hydrocarbon compounds that contain at least one carbon-carbon double bond within a ring structure. In the correct choice, Cyclobutene, the molecule features a four-carbon ring where one of the carbon-carbon bonds is a double bond, embodying the characteristics of both a cyclic and alkene structure.

Butene is a straight-chain alkene with no rings, simply containing a double bond between two carbons. Cyclopentane is a cyclic compound but is completely saturated with single bonds, hence not an alkene. Hexene is another straight-chain alkene similar to butene, devoid of any cyclic structure. Therefore, Cyclobutene stands out as it satisfies the requirements of being both cyclic and having a double bond, making it the correct answer.