Approximately what percentage of the Earth's atmosphere is made up of oxygen?

The correct answer is 21% because the composition of the Earth's atmosphere is approximately 78% nitrogen and about 21% oxygen. This percentage is consistent with established scientific measurements and data on atmospheric composition. Understanding that oxygen makes up roughly one-fifth of the atmosphere is crucial for various applications, including medical gas practices. In healthcare, the availability of oxygen is vital for patient care, especially in situations requiring supplemental oxygen. Knowing the exact composition helps healthcare professionals understand the environmental conditions and ensures compliant practices in administering medical gases.