What is the minimum percentage of oxygen required to maintain compatibility with life?

The minimum percentage of oxygen required to maintain compatibility with life is approximately 21%. This concentration is crucial because it reflects the normal atmospheric oxygen level that human beings, along with most other aerobic organisms, thrive on. At this level, oxygen is sufficiently available for the processes of respiration, which is essential for cellular metabolism and overall physiological function.

When oxygen levels drop below this threshold, individuals may begin to experience symptoms of hypoxia, which can lead to serious health complications and, if prolonged, can be life-threatening. For instance, at around 15% oxygen, individuals may suffer from significant cognitive and physical impairment, and levels below this can result in loss of consciousness and eventually death.

The options below 21% do not provide enough oxygen to support human life adequately under normal atmospheric conditions. Therefore, the choice reflecting 21% accurately signifies the safe and necessary concentration of atmospheric oxygen needed for sustaining life.