Step 1: Understanding the Question:
The problem asks us to compare boiling points of four organic compounds (an amine, a carboxylic acid, an alcohol, and a branched alkane) with similar molecular weights and identify the highest one.
Step 2: Key Formula or Approach:
Boiling point depends on intermolecular force strength. The hierarchy from strongest to weakest is: Extensive H-bonding>Standard H-bonding>Dipole-dipole>London dispersion forces.
Step 3: Detailed Explanation:
Option (D) isopentane has only weak London forces, so it boils lowest. Option (A) butylamine forms H-bonds via -NH₂, but N is less electronegative than O, making these bonds weaker. Option (C) butan-1-ol has a polarized -OH group enabling strong H-bonding. Option (B) propanoic acid possesses a -COOH group that forms stable cyclic dimers through two strong H-bonds per pair, persisting even in vapor, giving it the highest boiling point among all.
Step 4: Final Answer:
Propanoic acid (C₂H₅COOH) exhibits the highest boiling point due to exceptional H-bonding capability, matching option (B).