How much oxygen is contained in one liter of air?

In one liter of air at standard temperature and pressure (STP), approximately 21% of the air is oxygen. This can be calculated using the molecular weight of oxygen and the composition of air. The total weight of one liter of air is roughly 1.3 grams, so 21% of that translates into around 285 mg of oxygen. This conversion is significant when considering the role of oxygen in various processes, including animal respiration and combustion.

Understanding the atmospheric composition is critical, especially in the context of brewing and fermentation, as the amount of oxygen can impact yeast performance and beer quality. While the other options provide figures that are close, they do not accurately reflect the standard calculation based on the composition of air. The precise amount of oxygen is crucial in specific applications such as brewing, where oxygen levels need to be managed carefully to prevent oxidative spoilage or off-flavors.