Which among the following has higher boiling point?

Boiling points in a homologous series depend primarily on molecular weight and the resulting London dispersion forces. All aldehydes exhibit dipole-dipole interactions but cannot form intermolecular hydrogen bonds.

Molecular weights increase as follows: ethanal (2 carbons), propanal (3 carbons), pentanal (5 carbons), hexanal (6 carbons). With increasing molecular weight, surface area and dispersion forces strengthen, requiring more energy to vaporize.

Hexanal has the highest molecular weight and thus the strongest intermolecular forces, resulting in the highest boiling point.