The gas mixture contains 300 molecules of oxygen O2 and 200 molecules of ozone O3

The gas mixture contains 300 molecules of oxygen O2 and 200 molecules of ozone O3. How many oxygen atoms are there in this mixture?

Each O2 molecule contains two (2) oxygen atoms, and each ozone O3 molecule contains three (3) atoms. In order to calculate the total number of oxygen atoms, you need to multiply the number of oxygen molecules by 2 (this is how we find the number of atoms in oxygen) and add the number of ozone molecules multiplied by 3 (the number of oxygen atoms in ozone)
Accordingly, the number of oxygen atoms is 300 * 2 + 200 * 3 = 1200
Answer: The mixture contains 1200 oxygen atoms.