Question

The element present in the highest proportion (about 65% by mass) in the human body is:

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

Hint:

Think about which element dominates the mass of water and organic tissue.

Answer 1

The Correct Option is C

The human body is made up mostly of water and organic compounds, and its elemental composition by mass is dominated by a few elements.

Step 1: Oxygen makes up close to 65 percent of body mass. Water forms about 60 to 65 percent of the body, and water is rich in oxygen by weight, since each water molecule has 16 parts oxygen to only 2 parts hydrogen by mass. Oxygen is also present in proteins, carbohydrates, fats and bone minerals.

Step 2: Carbon comes next at around 18 percent, because it is the backbone of all organic molecules like proteins, fats, carbohydrates and DNA.

Step 3: Hydrogen is about 10 percent, mostly from water and organic compounds, and nitrogen is about 3 percent, mainly from proteins and nucleic acids.

Step 4: Comparing the four options, oxygen has the largest share of body mass, so the correct choice is option C.