Advanced Placement (AP) Chemistry Practice Exam

An alkane is defined as a saturated hydrocarbon that contains only single carbon-carbon bonds. This characteristic of containing only single bonds means that each carbon atom is bonded to the maximum number of hydrogen atoms possible, leading to a general formula of CₙH₂ₙ₊₂. This saturation is critical because it distinguishes alkanes from alkenes (which contain double bonds) and alkynes (which contain triple bonds).

In contrast, hydrocarbons with double or triple bonds, such as those described in the other options, do not fit the alkane definition. For instance, alkenes contain at least one carbon-carbon double bond, making them unsaturated, while alkynes feature at least one carbon-carbon triple bond, also rendering them unsaturated. The option suggesting that a hydrocarbon with only branched chains defines an alkane fails to recognize that alkanes can be either straight-chain or branched, and being branched alone doesn't define the alkane class. Therefore, the definition in the correct choice correctly emphasizes the saturated nature and single bonds present in alkanes.