Which from following compounds has highest boiling point?

Boiling points in organic compounds are governed by intermolecular force strength. Among homologous aldehyde series, increasing molecular weight and chain length enhance London dispersion interactions.

Molecular weights are calculated as follows: acetaldehyde (C₂H₄O) $\mathrm{MW} = 44.06$ g/mol, propionaldehyde (C₃H₆O) $\mathrm{MW} = 58.09$ g/mol, butyraldehyde (C₄H₈O) $\mathrm{MW} = 72.12$ g/mol, and valeraldehyde (C₅H₁₀O) $\mathrm{MW} = 86.15$ g/mol.

Valeraldehyde possesses the greatest molecular mass and longest carbon chain, resulting in the most substantial London dispersion forces. These stronger interactions necessitate higher energy input for phase transition, correlating with an elevated boiling point.

Answer: $\boxed{\text{D}}$