What is the normal concentration of oxygen in the air?

The normal concentration of oxygen in the air is approximately 21%. This value is a crucial piece of information in various fields, such as environmental science, medicine, and aviation, as it directly affects the breathing and functioning of humans and many other organisms.

Understanding this concentration is essential because oxygen levels around this percentage support life, allowing for efficient respiration. Deviations from this concentration, such as significantly lower levels, can lead to hypoxia, a condition where body tissues do not receive enough oxygen, potentially resulting in serious health issues.

In the context of the other choices, 78% represents the concentration of nitrogen, which is the primary component of Earth's atmosphere. The choices of 30% and 15% are not indicative of normal atmospheric conditions and would suggest an environment either nearly saturated with oxygen or oxygen-deprived, both of which are not typical for Earth's atmosphere at sea level.