Lower aliphatic amines, such as methylamine, ethylamine, and propylamine, exhibit a trend in physical states and odors based on increasing molecular size. As the alkyl chain length increases, the physical state changes from gases (e.g., methylamine) to liquids (e.g., ethylamine) and eventually to solids (e.g., propylamine) at room temperature. Additionally, the odor becomes more offensive with increasing alkyl chain length. Methylamine has a pungent fishy odor, ethylamine has an ammonia-like odor, and propylamine possesses an unpleasant, putrid odor. This trend reflects the influence of molecular size on intermolecular forces and volatility, impacting physical properties and olfactory characteristics.