Which two elements are both among the six most common elements of life?

Which two elements are both among the six most common elements of life?

• A. Carbon and Sulfur
• B. Sodium and Neon
• C. Iron and Copper
• D. Silicon and Titanium

Answer: (A)

The idea here is that life relies on a small, very common set of elements—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS). Carbon is central because it can form long, diverse backbones for all the major organic molecules—carbohydrates, lipids, proteins, and nucleic acids—by making four covalent bonds and building complex structures. Sulfur, while not as abundant as carbon, is still essential across biology: it appears in certain amino acids and cofactors and helps stabilize protein shapes through disulfide bonds, playing important roles in enzyme function. Since both carbon and sulfur are part of CHNOPS, they are two of the six most common elements found in living organisms. The other options include elements that are either not as abundant in biology or not routinely incorporated into biomolecules on the same scale (neon is a noble gas and not used in biology; sodium is important but not among the top six by mass; iron and copper are trace elements; silicon and titanium are not common building blocks in biology).

The idea here is that life relies on a small, very common set of elements—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS). Carbon is central because it can form long, diverse backbones for all the major organic molecules—carbohydrates, lipids, proteins, and nucleic acids—by making four covalent bonds and building complex structures. Sulfur, while not as abundant as carbon, is still essential across biology: it appears in certain amino acids and cofactors and helps stabilize protein shapes through disulfide bonds, playing important roles in enzyme function. Since both carbon and sulfur are part of CHNOPS, they are two of the six most common elements found in living organisms. The other options include elements that are either not as abundant in biology or not routinely incorporated into biomolecules on the same scale (neon is a noble gas and not used in biology; sodium is important but not among the top six by mass; iron and copper are trace elements; silicon and titanium are not common building blocks in biology).