What characteristic of unsaturated fatty acids contributes to their liquid state at room temperature?

The characteristic of unsaturated fatty acids that contributes to their liquid state at room temperature is the presence of double bonds. Unsaturated fatty acids contain one or more double bonds between carbon atoms in their hydrocarbon chain. These double bonds introduce kinks or bends in the structure of the fatty acid. As a result, the molecules cannot pack closely together, which decreases the intermolecular forces, such as van der Waals forces, that hold the fatty acid chains together when in a solid state.

This inability to pack tightly leads to a lower melting point, allowing unsaturated fatty acids to remain liquid at room temperature. In contrast, saturated fatty acids, which do not have double bonds, can pack closely together, leading to a more substantial intermolecular attraction and a solid state at room temperature. The physical state of a fatty acid, whether solid or liquid, is fundamentally influenced by whether it is saturated or unsaturated, illustrating the significance of double bonds in determining these properties.