Which set lists the six most common elements of life?

• A. carbon, hydrogen, nitrogen, oxygen, calcium, sulfur
• B. carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur
• C. carbon, helium, lithium, oxygen, phosphorus, sulfur
• D. carbon, hydrogen, nitrogen, neon, phosphorus, sulfur

Answer: (B)

Life relies on a small set of elements that form the vast majority of biological molecules. The six most common are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—often remembered as CHNOPS. Carbon provides the backbone for organic molecules, allowing long chains and rings to build carbohydrates, proteins, fats, and nucleic acids. Hydrogen and oxygen are major parts of water and a huge variety of organic compounds, enabling the diverse bonding that shapes complex structures. Nitrogen is essential for amino acids and nucleotides, the building blocks of proteins and DNA/RNA. Phosphorus is crucial for nucleic acids and energy transfer molecules like ATP. Sulfur appears in certain amino acids and vitamins, contributing to the structure and function of some proteins. Other elements on the choices, such as calcium or noble gases like helium and neon, aren’t found in as large amounts in living matter or don’t participate in the core organic chemistry of life, so they don’t belong to the six most common. That’s why the set including carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur best represents life’s fundamental elements.