Which macronutrient is primarily involved in the structural components of proteins and nucleic acids?

The correct answer is carbon, as it serves as a fundamental building block for both proteins and nucleic acids. Proteins are composed of amino acids, which contain carbon atoms as part of their structure. Similarly, nucleic acids, such as DNA and RNA, are made up of nucleotides that also include carbon. Carbon's ability to form stable covalent bonds with other elements, including hydrogen, oxygen, nitrogen, and phosphorus, allows it to create a diverse range of complex organic molecules, essential for life.

In contrast, while sodium, potassium, and iron play critical roles in biological systems—such as in enzyme function, ion balance, and oxygen transport—they do not serve as primary structural components of proteins and nucleic acids like carbon does.