Which atom is NOT found in lipids?

Lipids are a diverse group of organic compounds that are primarily composed of carbon, hydrogen, and oxygen atoms. The structure of lipids generally includes long hydrocarbon chains or ring structures that are rich in hydrogen and carbon. While oxygen is also a component of many lipids, especially in glycerol and fatty acids, nitrogen is not typically present in standard lipid structures.

Most common classes of lipids, such as triglycerides (fats and oils) and phospholipids, consist of glycerol (which contains carbon, hydrogen, and oxygen) and fatty acids (which predominantly have carbon and hydrogen). The presence of nitrogen would indicate amino acids or nucleotides, which are components of proteins and nucleic acids rather than lipids. Therefore, in the context of standard lipid composition, nitrogen is not an element found in typical lipids, making it the correct choice in identifying which atom is not associated with them.