(C) C₃H₈
C₃H₈ is a saturated hydrocarbon (alkane). Saturated hydrocarbons undergo substitution reactions, not addition reactions. Only unsaturated compounds (alkenes, alkynes) undergo addition reactions.
The key concept: addition reactions occur only in unsaturated hydrocarbons (those with double or triple bonds). C₄H₈ (alkene), C₂H₂ (alkyne), and C₂H₄ (alkene) are all unsaturated — they have C=C or C≡C bonds and readily undergo addition. C₃H₈ is propane, a saturated alkane; it undergoes substitution, not addition. Examiners expect you to identify the saturated compound by its general formula CₙH₂ₙ₊₂.