Calculate the mass percentage of oxygen in dry air.Express your answer with the appropriate units.

The composition of dry air is approximately 78% nitrogen, 21% oxygen, and 1% other gases.

To calculate the mass percentage of oxygen in dry air, we need to know the molecular weights of nitrogen (N2), oxygen (O2), and the other gases.

The molecular weight of nitrogen (N2) is approximately 28 grams per mole, and the molecular weight of oxygen (O2) is approximately 32 grams per mole.

Since dry air is about 21% oxygen, we can calculate the mass of oxygen in 100 grams of air as follows:

Mass of oxygen = 21/100 * 100 g = 21 g

Therefore, the mass percentage of oxygen in dry air is 21%.