What is the approximate percentage and partial pressure of oxygen (O₂) in the atmosphere at sea level?

The approximate percentage and partial pressure of oxygen in the atmosphere at sea level is indeed 21% and approximately 160 mmHg, respectively. At sea level, the total atmospheric pressure is around 760 mmHg. The partial pressure of a gas can be calculated by multiplying the total atmospheric pressure by the fraction of that gas in the atmosphere. Since oxygen constitutes about 21% of the atmosphere, the calculation would be:

0.21 (fraction of O₂) × 760 mmHg (total atmospheric pressure) = approximately 160 mmHg.

This value is essential in understanding how gases behave in respiration and the physiological implications of oxygen availability at different altitudes. It’s important for various medical and ecological applications, including those involving oxygen therapy and treatments related to hypoxia or high-altitude sickness. The other responses reflect incorrect values for the concentration and consequent partial pressures of oxygen in the atmosphere.