Which element is NOT among the six most common elements of life?

Which element is NOT among the six most common elements of life?

• A. Sodium
• B. Carbon
• C. Oxygen
• D. Nitrogen

Answer: (A)

Think about the elements that make up most biomolecules. The six most common in living organisms are carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Sodium isn’t part of that main group; it’s a divalent ion that’s essential for some cellular processes and nerve signaling, but it doesn’t form the backbone of biomolecules the way the CHNOPS elements do. So the element not among the six is sodium. The other elements listed—carbon, hydrogen, oxygen, and nitrogen—are all core components of biomolecules, with phosphorus and sulfur also key in DNA/RNA, ATP, and certain amino acids.

Think about the elements that make up most biomolecules. The six most common in living organisms are carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Sodium isn’t part of that main group; it’s a divalent ion that’s essential for some cellular processes and nerve signaling, but it doesn’t form the backbone of biomolecules the way the CHNOPS elements do. So the element not among the six is sodium. The other elements listed—carbon, hydrogen, oxygen, and nitrogen—are all core components of biomolecules, with phosphorus and sulfur also key in DNA/RNA, ATP, and certain amino acids.