Final answer:
Oxygen is the element that comprises the greatest percent of the human body, making up about 50% of a cell's composition.
Step-by-step explanation:
The element that comprises the greatest percent of the human body is Oxygen (O). Oxygen is a major component of all macromolecules and makes up about 50% of a cell's composition. This prevalence is not because of its abundance on Earth, but rather because of its availability in a form that can be assimilated by the human body.
We obtain oxygen from the air we breathe and the water we drink. The four most common elements in living organisms are oxygen, carbon, hydrogen, and nitrogen, which together comprise 96% of living organisms, with oxygen being the most abundant among them.