Name the molecule C3H8.

Name the molecule C3H8.

• A. Methane
• B. Ethane
• C. Propane
• D. Butane

Answer: (C)

Understanding how names reflect carbon count helps here. The general formula for alkanes is CnH2n+2, so for n = 3 you get C3H8. The three-carbon alkane is named propane, using the prefix prop- for three carbons and the -ane ending for a saturated hydrocarbon. A quick look at the structure CH3-CH2-CH3 confirms three carbon atoms arranged in a chain with the remaining hydrogens saturating the valences. There’s no branching for three carbons, so only one isomer exists. Compared to methane (one carbon) and ethane (two carbons) and butane (four carbons), C3H8 matches three carbons, so propane is the correct name.

Understanding how names reflect carbon count helps here. The general formula for alkanes is CnH2n+2, so for n = 3 you get C3H8. The three-carbon alkane is named propane, using the prefix prop- for three carbons and the -ane ending for a saturated hydrocarbon. A quick look at the structure CH3-CH2-CH3 confirms three carbon atoms arranged in a chain with the remaining hydrogens saturating the valences. There’s no branching for three carbons, so only one isomer exists. Compared to methane (one carbon) and ethane (two carbons) and butane (four carbons), C3H8 matches three carbons, so propane is the correct name.