Final answer:
The intermolecular forces present in each substance are determined by their molecular structure: C₃H₈ experiences London dispersion forces, CH₃OH experiences dipole-dipole forces and hydrogen bonding, and H₂S experiences dipole-dipole forces. Methanol is a liquid at room temperature due to its stronger intermolecular forces.
Step-by-step explanation:
The intermolecular forces present in each substance can be determined based on their molecular structure. C₃H₈ (propane) is a nonpolar molecule and only exhibits London dispersion forces. CH₃OH (methanol) is a polar molecule and experiences both dipole-dipole forces and hydrogen bonding. H₂S (hydrogen sulfide) is also a polar molecule and has dipole-dipole forces.
Out of these substances, CH₃OH (methanol) is a liquid at room temperature because of the stronger intermolecular forces compared to the other two.