Which element is not among the four major elements by weight?

Which element is not among the four major elements by weight?

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

Answer: (D)

Biological mass is dominated by four elements: hydrogen, carbon, nitrogen, and oxygen. Hydrogen and oxygen come largely from water and many organic compounds; carbon provides the backbone for almost all biomolecules; nitrogen is a key part of proteins and nucleic acids. Sodium, while essential for nerve signaling and fluid balance, is present only in much smaller amounts and does not contribute significantly to the mass of the body. So among the options, sodium is not one of the four major elements by weight.

Biological mass is dominated by four elements: hydrogen, carbon, nitrogen, and oxygen. Hydrogen and oxygen come largely from water and many organic compounds; carbon provides the backbone for almost all biomolecules; nitrogen is a key part of proteins and nucleic acids. Sodium, while essential for nerve signaling and fluid balance, is present only in much smaller amounts and does not contribute significantly to the mass of the body. So among the options, sodium is not one of the four major elements by weight.