Final answer:
The mass of oxygen in a cubic meter of air in a typical classroom at 1 atm and 25°C is 268.8 grams.
Step-by-step explanation:
The mass of oxygen in a cubic meter of air in a typical classroom can be calculated using the given composition of Earth's atmosphere. According to the question, the atmosphere is approximately 78.0% nitrogen and 21.0% oxygen. We can assume that the remaining 1.0% is made up of other gases.
Using the information that the mass of one cubic meter of air is 1.28 kg, we can calculate the mass of oxygen by multiplying the mass of air by the percent composition of oxygen. Therefore, the mass of oxygen in a cubic meter of air in a typical classroom at 1 atm and 25°C is:
Mass of oxygen = (Percentage of oxygen / 100) x Mass of air
Mass of oxygen = (21.0 / 100) x 1.28 kg = 0.2688 kg = 268.8 grams.