1. **State the problem:** Calculate the relative formula mass of sodium fluoride (NaF). 2. **Formula used:** The relative formula mass is the sum of the relative atomic masses of all atoms in the formula. 3. **Given data:** - Relative atomic mass of sodium (Na) = 23 - Relative atomic mass of fluorine (F) = 19 4. **Calculate:** $$\text{Relative formula mass of NaF} = A_r(\text{Na}) + A_r(\text{F})$$ 5. **Substitute values:** $$= 23 + 19$$ 6. **Add:** $$= 42$$ 7. **Conclusion:** The relative formula mass of sodium fluoride (NaF) is 42.