Which of the following is the general formula of alkenes?

CnH2n is the general formula of alkenes. Alkenes are unsaturated hydrocarbons having at least one double bond where n is the number of carbon atoms. CnH2n+1 is the general formula for alkyl groups, not alkenes. C2nH2n shows that carbon atoms double each time, which is not the correct pattern for alkenes. CnHn is incorrect as the number of hydrogen atoms is double the number of carbon in alkenes.