Final answer:
An unsaturated fatty acid has one or more places on its chemical chain in which hydrogen is missing. Monounsaturated fatty acids have one double bond, while polyunsaturated fatty acids have two or more double bonds.
Step-by-step explanation:
An unsaturated fatty acid has one or more places on its chemical chain in which hydrogen is missing. These points of unsaturation occur when there is a double bond between carbon atoms in the fatty acid. Monounsaturated fatty acids have one double bond, while polyunsaturated fatty acids have two or more double bonds. Examples of unsaturated fatty acids include oleic acid and stearic acid.