A fatty acid is named omega-3 when the:

1. Numbering starts from the carbon farthest from the carboxyl group, called the omega carbon. 2. The name records where the first double bond sits counting from that end. 3. In an omega-3 acid the third carbon from the end of the hydrocarbon chain is joined to its neighbour by a double bond. 4. The double bond therefore lies between the third and fourth carbon from the omega end. 5. Option A confuses position with count, and option D swaps both the end and the functional group. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 3 'Biological Macromolecules', sections 3.1-3.5_