The hydrocarbons listed are alkanes, which follow the general formula CnH2n+2. The order of increasing 'n' is methane (n=1), ethane (n=2), propane (n=3), and butane (n=4). Since each additional carbon atom (atomic weight ~12) and two hydrogen atoms (atomic weight ~1 each) add approximately 14 to the molecular weight, the molecular weights increase directly with the number of carbon atoms in this series. - Methane (CH₄): MW ≈ 12 + 4(1) = 16 - Ethane (C₂H₆): MW ≈ 2(12) + 6(1) = 24 + 6 = 30 - Propane (C₃H₈): MW ≈ 3(12) + 8(1) = 36 + 8 = 44 - Butane (C₄H₁₀): MW ≈ 4(12) + 10(1) = 48 + 10 = 58