Which class of hydrocarbons contains only single bonds and has the formula CnH2n+2?

• A. Alkene
• B. Alkyne
• C. Alkane
• D. Aromatic

Answer: (C)

Saturation in hydrocarbons means all carbon–carbon bonds are single bonds, so the molecule holds the maximum number of hydrogens. For an open-chain alkane with n carbons, the hydrogens follow H = 2n + 2. This comes from counting how many bonds each carbon needs to satisfy valence: with only single bonds, the carbon network ends up needing two extra hydrogens per carbon pair and two additional hydrogens overall, giving the familiar CHn+2 pattern. Examples—methane (CH4), ethane (C2H6), propane (C3H8)—fit this formula, and the pattern continues for larger alkanes.

Alkenes have at least one carbon–carbon double bond, which reduces the hydrogen count to CnH2n. Alkynes have a carbon–carbon triple bond, giving CnH2n−2. Aromatic hydrocarbons are unsaturated due to ring structures and delocalized pi bonds, so they do not follow the CnH2n+2 rule (benzene, for instance, is C6H6).