Which nonmetallic element is found in all living things?

The correct answer is carbon because it is a fundamental building block of life. All known forms of life on Earth are based on carbon-based molecules. This includes the complex organic compounds that make up proteins, nucleic acids (like DNA and RNA), carbohydrates, and lipids, which are essential for cellular structure and function.

Carbon has unique properties that allow it to form stable covalent bonds with many elements, including itself. This enables the creation of a vast array of diverse structures, ranging from simple hydrocarbons to complex macromolecules. The diversity of carbon compounds is what allows biological systems to perform a wide variety of functions, from energy storage to catalyzing metabolic reactions.

Although nitrogen, oxygen, and hydrogen are also critical to biological processes and are present in many biological molecules, none are as versatile and central to the structure and function of living organisms as carbon.