What is the general formula for alkenes?

The correct answer is based on the structural characteristics of alkenes, which are hydrocarbons that contain at least one carbon-carbon double bond. The general formula for alkenes is CnH2n, where 'n' represents the number of carbon atoms in the molecule. This formula indicates that for every n carbon atoms, there are 2n hydrogen atoms, reflecting the presence of the double bond, which reduces the number of hydrogen atoms compared to alkanes, which follow the formula CnH2n+2.

Alkenes are unsaturated compounds, meaning they have fewer hydrogen atoms than their saturated counterparts (alkanes) due to the presence of the double bond. This is why the other options do not apply. For example, CnH2n+2, which applies to alkanes, would imply a saturated structure with maximum hydrogen saturation. CnH2n-2 and CnH2n-1 do not accurately represent the relationship of hydrogen atoms in alkenes, as they suggest a different structure or fewer hydrogen atoms that do not correspond to those found in alkenes' general formula. Thus, CnH2n is the appropriate representation for alkenes.