Which percentage indicates normal oxygen levels in the atmosphere?

• A. 19.5%
• B. 20%
• C. 20.9%
• D. 22%

Answer: (C)

Normal oxygen levels in the atmosphere are represented by a concentration of approximately 20.9%. This percentage reflects the average amount of oxygen present in the Earth's atmosphere, which is essential for sustaining life and supporting various biological processes.

It's important to note that while options like 20% and 19.5% might seem close, they do not accurately reflect the standard atmospheric composition that is commonly accepted. The value of 22% exceeds the typical percentage found in the atmosphere and may suggest a hyperoxic environment, which can have different implications for health and safety. Therefore, the most accurate representation of normal atmospheric oxygen levels is 20.9%.