15. The major constituent of air is A.Nitrogen B.Carbon dioxide C.Oxygen D.Hydrogen
Answer: Option A Solution: Below a height of about 86 kilometers, the three main gaseous elements, which together account for about 99.9% of the total atmosphere, exist in essentially constant proportion to the total: nitrogen comprises 78% of air by volume, oxygen comprises 21% of air by volume, and argon comprises another 0.9%.
