The correct answer is d) carbon. Organic compounds are defined as compounds that contain carbon atoms. This is the fundamental aspect that distinguishes organic chemistry from inorganic chemistry.
Carbon has the unique ability to form stable bonds with many elements, including itself, which allows for a diverse array of complex molecules. Every organic compound, whether it’s carbohydrates, proteins, lipids, or nucleic acids, contains carbon as a key element. While phosphorus, nitrogen, and oxygen are also important in various organic molecules, they are not present in all organic compounds.