Oxygen is a gas that forms 21% of the total atmosphere of Earth.
What is the significance of Oxygen?
Oxygen is a colorless and odorless gas, which is the only gas regarded as suitable for human consumption. It comprises the second-highest content of the Earths' atmospheric gases.
Hence, option D holds true that oxygen forms 21% of Earth's atmosphere.
Learn more about oxygen here:
https://brainly.com/question/13370320
#SPJ2
