Answer:
The correct answer will be- Oxygen (21%) and Nitrogen (78%)
Step-by-step explanation:
The atmosphere of Earth is composed of a mixture of the gases in different concentrations.
The major constituent gases of the atmosphere are the nitrogen which constitutes about 78% of the total gases present and the oxygen which constitutes the 21% of the total gases.
These gases exist in their divalent states in the atmosphere where the nitrogen is used by the organisms when it is fixed by the prokaryotic nitrogen-fixing bacteria whereas the oxygen is directly used by the organism.
Thus, Oxygen (21%) and Nitrogen (78%) is the correct answer.