The correct answer is: CnH2n.
Alkenes are unsaturated hydrocarbons that have a double bond between two carbon atoms. The general formula for alkenes is CnH2n, where n is the number of carbon atoms in the molecule. The simplest alkene is ethene, which has the formula C2H4. Other common alkenes include ethane, propene, and butene.
Alkenes are important in organic chemistry because they can be used to make a variety of products, including plastics, gasoline, and solvents. They are also found in natural gas and petroleum.
The other options are incorrect because they do not represent the general formula for alkenes. Option A, CnH2n + 2, is the general formula for alkanes, which are saturated hydrocarbons that do not have any double bonds. Option B, CnH2n – 1, is the general formula for alkynes, which are unsaturated hydrocarbons that have a triple bond between two carbon atoms. Option C, CnH2n + 1, is not the general formula for any type of hydrocarbon.