Which fatty acids typically contain a long chain of carbon atoms ranging from 2 to 22?

Free fatty acids are the correct answer because they refer to fatty acids that are not attached to any other molecule and can vary significantly in chain length. They are classified based on the length of their carbon chains. Typically, free fatty acids have chains that can range from as few as 2 carbons to as many as 22 or more. This wide range includes both saturated and unsaturated varieties of fatty acids.

Polyunsaturated fatty acids specifically refer to fatty acids that contain multiple double bonds in their carbon chains, and while they may also be long-chain, the term does not inherently denote the chain length. Saturated fatty acids are a subset of fatty acids that have no double bonds, but again, their classification does not specify the carbon chain length, as they can be found in both short and long forms. Trans fatty acids can also be long-chain, but they are specifically a type of unsaturated fatty acid with a specific configuration of hydrogen atoms around the double bonds, not defined by their carbon chain length.

Thus, while other types of fatty acids can contain long chains, the term "free fatty acids" encompasses the broad spectrum of carbon chain lengths, including those that range from 2 to 22 carbon atoms.