Question 3
By mass, which element makes up the largest share of the human body?
The right answer is the one marked above.
Oxygen, at about 65%. Carbon follows at 18%, hydrogen at 10% and nitrogen at 3%; everything else together comes to roughly 4%.
Oxygen leads because so much of a body is water, and water is mostly oxygen by mass. Oxygen is found in all the fluids, the tissues, the bones and the proteins.