Boiling points depend on intermolecular forces for similar-sized molecules

Steps:

• Identify molecular weights (MW) for each pair to find comparable sizes.
• For similar MW, stronger forces (e.g., hydrogen bonding) raise boiling point over London dispersion.
• Compare pairs: polar/hydrogen-bonding compounds have higher BP than nonpolar of similar MW.
• Select pair where first has hydrogen bonding and second lacks it, making second's BP lower.

Why D is correct:

• CH₃OH (MW 32) forms hydrogen bonds, while CH₃CH₃ (MW 30) has only London forces; by definition, hydrogen bonding increases BP (65°C vs. -89°C).

Why the others are wrong:

• A: Similar MW (~44–46), but CH₃CH₂OH has hydrogen bonding, raising its BP above CH₃CH₂CH₃.
• B: Ar (MW 40) has higher BP than Ne (MW 20) due to stronger London forces from larger size.
• C: CH₄ (MW 16) much smaller than CH₃NH₂ (MW 31), so lower BP expected from size, not force comparison.

Final answer: D