Hydrogen bonding and molecular size determine boiling points

Steps:

• Identify intermolecular forces: alcohols (methanol, ethanol) form hydrogen bonds due to -OH groups; methoxymethane (ether) only has dipole-dipole and London forces.
• Compare methoxymethane to alcohols: lacks hydrogen bonding, so lowest boiling point.
• Compare methanol and ethanol: both form hydrogen bonds, but ethanol's larger size increases van der Waals forces, raising its boiling point above methanol's.
• Conclude ethanol has the highest boiling point due to strongest overall intermolecular attractions.

Why C is correct:

• Ethanol forms hydrogen bonds (O-H...O) and has higher molecular weight (46 g/mol vs. methanol's 32 g/mol), leading to the highest boiling point per intermolecular force hierarchies.

Why the others are wrong:

• A: Ethanol's hydrogen bonding exceeds permanent dipole-dipole forces in strength.
• B: Methanol forms hydrogen bonds but has lower molecular weight, so lower boiling point than ethanol.
• D: Same as A; ignores ethanol's dominant hydrogen bonding.

Final answer: C