What is the approximate percentage of oxygen in the atmosphere?

The approximate percentage of oxygen in the atmosphere is 21%. This is a well-established fact in atmospheric science and chemistry, indicating that oxygen constitutes about one-fifth of the Earth's atmosphere. The significance of this oxygen level is crucial for the survival of aerobic organisms, including humans, as it is essential for respiration.

At sea level, the atmosphere consists of approximately 78% nitrogen, with oxygen making up nearly 21%, along with trace amounts of other gases. Understanding these proportions is vital, as they play a significant role in various natural processes, including combustion, respiration, and the greenhouse effect. The atmosphere's composition directly influences climate, weather patterns, and ecological systems.

The other options significantly misrepresent the actual percentage of oxygen, which would impact comprehension about atmospheric conditions and gas exchanges occurring in the environment.