Final answer:
An unsaturated fatty acid has at least one double bond between carbon atoms; monounsaturated has one, and polyunsaturated has two or more. Example of monounsaturated is oleic acid.
Step-by-step explanation:
A fatty acid that has at least one double bond between adjacent carbon atoms is called an unsaturated fatty acid. A monounsaturated fatty acid has one double bond, while a polyunsaturated fatty acid contains two or more double bonds. Oleic acid is an example of a monounsaturated fatty acid.
When there are double bonds in a fatty acid, the hydrocarbon chain cannot hold as many hydrogen atoms, resulting in bends or "kinks" at the site of the double bonds.
These unsaturated fatty acids do not pack together as tightly compared to saturated fatty acids, which have no double bonds and are often solid at room temperature. Contrastingly, unsaturated fatty acids tend to be liquid at room temperature. Notably, olive oil is composed of both mono- and polyunsaturated fatty acids.