UPSC 2016 CDS II GK Paper

The elemental composition of an adult human body by mass is O > C > H > N. Almost 99% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus. Only about 0.85% is composed of the other five elements: potassium, sulphur, sodium, chlorine and magnesium. Oxygen constitutes 65%, carbon 18%, hydrogen 10% and nitrogen 3%.