Which type of fatty acid has one or more double bonds in its carbon chain?

The correct answer is that both monounsaturated and polyunsaturated fatty acids contain one or more double bonds in their carbon chains.

Monounsaturated fatty acids have one double bond present in their structure. This dual nature impacts their physical properties, such as state at room temperature; they generally tend to be liquid at room temperature due to the presence of the double bond, which creates a kink in the fatty acid chain, preventing tight packing.

Polyunsaturated fatty acids, on the other hand, have two or more double bonds in their carbon chain. Like monounsaturated fats, they are also typically liquid at room temperature. The multiple double bonds also influence their nutritional properties and their role in health, contributing to the recommendations for including these types of fats in a balanced diet.

Saturated fatty acids, in contrast, possess no double bonds in their carbon chains, making them fully "saturated" with hydrogen atoms. This saturation results in a more solid structure at room temperature, which is a notable difference compared to both monounsaturated and polyunsaturated fatty acids. Thus, the presence of one or more double bonds is the defining feature of monounsaturated and polyunsaturated fatty acids, confirming why the answer includes both categories.