Final answer:
Unsaturated fatty acids have lower melting points due to the presence of double bonds, which cause a kink or bend in the carbon chain. This prevents the molecules from packing closely together, resulting in weaker intermolecular attractions and lower melting points.
Step-by-step explanation:
Unsaturated fatty acids have lower melting points due to the presence of double bonds between carbon atoms. The double bonds create a kink or bend in the carbon chain, preventing the molecules from packing closely together.
As a result, the intermolecular attractions among unsaturated fatty acids are weaker, leading to lower melting points. For example, saturated fatty acids are solids at room temperature, while unsaturated fatty acids are liquids.