Which elements make up about 90% of the weight of the human body?

• A. Oxygen, Hydrogen, Carbon, Nitrogen
• B. Oxygen, Nitrogen, Phosphorus, Sulfur
• C. Hydrogen, Helium, Neon, Argon
• D. Sodium, Potassium, Calcium, Magnesium

Answer: (A)

The question tests which elements dominate the mass of the human body. Living matter is mostly water and organic molecules, so a few elements account for the vast majority of weight. Oxygen stands out as the largest contributor because it makes up much of water and of biomolecules; carbon forms the backbone of organic molecules; hydrogen is abundant in water and in organic compounds; and nitrogen is a major component of proteins and nucleic acids. Together, these four elements make up roughly 95–96% of body mass, which aligns with the idea of about 90%. The other elements mentioned are present but in much smaller amounts, while noble gases aren’t incorporated in meaningful quantities in the body.