1. **Problem 1: Calculate the relative formula mass of sodium oxide, Na₂O.** 2. The relative formula mass (Mr) is the sum of the relative atomic masses (Ar) of all atoms in the formula. 3. For Na₂O, there are 2 sodium (Na) atoms and 1 oxygen (O) atom. 4. Using the given Ar values: Ar(Na) = 23, Ar(O) = 16. 5. Calculate Mr(Na₂O): $$Mr = 2 \times 23 + 1 \times 16 = 46 + 16 = 62$$ 6. **Answer:** The relative formula mass of sodium oxide is 62. 7. **Problem 2: Calculate the relative formula mass of one molecule of oxygen, O₂.** 8. O₂ consists of 2 oxygen atoms. 9. Using Ar(O) = 16: $$Mr = 2 \times 16 = 32$$ 10. **Answer:** The relative formula mass of oxygen molecule O₂ is 32. 11. **Problem 3: Calculate the relative formula mass of one molecule of fluorine, F₂.** 12. F₂ consists of 2 fluorine atoms. 13. Given Ar(F) = 19: $$Mr = 2 \times 19 = 38$$ 14. **Answer:** The relative formula mass of fluorine molecule F₂ is 38.