What is the general formula for an alkene?

The general formula for an alkene is represented as CnH2n. This formula indicates that for every n number of carbon atoms present in the alkene, the number of hydrogen atoms will be twice that number minus two. This is because alkenes contain at least one carbon-to-carbon double bond, which reduces the maximum number of hydrogen atoms that can be attached to the carbon skeleton compared to alkanes, which are saturated hydrocarbons.

In alkenes, the presence of a double bond introduces an unsaturation in the molecule, leading to this unique structural characteristic that differentiates them from saturated hydrocarbons. This is fundamental to understanding the properties and reactivity of alkenes in organic chemistry.

The other options provided do not accurately represent the structural formula of alkenes. For instance, CnH2n+1 would suggest an additional hydrogen atom, which would not apply to the double-bonded structure of alkenes. The formula CnH2n-2 does not account for the necessary number of hydrogens related to the presence of double bonds, and CnH2nO introduces oxygen, indicating a different class of compounds, such as alcohols or ethers, rather than alkenes.