Explanation

A) Methane (CH₄) - Molecular weight = 16 g/mol
B) Ethane (C₂H₆) - Molecular weight = 30 g/mol
C) Propane (C₃H₈) - Molecular weight = 44 g/mol
D) Butane (C₄H₁₀) - Molecular weight = 58 g/mol

Correct Answer: D) Butane

Butane is the heaviest among the options listed, with a molecular weight of 58 g/mol.