Final answer:
Phosphoglycerides, including phosphatidic acid, are composed of glycerol, a phosphate group, and fatty acids. The phosphate group is attached to the third carbon atom of the glycerol backbone. Hence, 2) is correct.
Step-by-step explanation:
A phosphatidic acid, which is a type of phosphoglyceride, is composed of glycerol + 1 phosphate group + 2 fatty acids. The glycerol acts as the backbone, with the fatty acids attached to the first two carbon atoms, and the phosphate group attached to the third carbon atom.
The presence of the phosphate group gives the phosphoglyceride its unique properties in cell membranes.