1. **State the problem:** We want to find the mass of one molecule of PO3 using dimensional analysis. 2. **Identify the formula:** The mass of one molecule can be found by dividing the molar mass of the compound by Avogadro's number. $$\text{Mass of one molecule} = \frac{\text{Molar mass of PO}_3}{\text{Avogadro's number}}$$ 3. **Calculate molar mass of PO3:** - Atomic mass of P (Phosphorus) = 30.97 g/mol - Atomic mass of O (Oxygen) = 16.00 g/mol $$\text{Molar mass of PO}_3 = 30.97 + 3 \times 16.00 = 30.97 + 48.00 = 78.97 \text{ g/mol}$$ 4. **Use Avogadro's number:** $$N_A = 6.022 \times 10^{23} \text{ molecules/mol}$$ 5. **Calculate mass of one molecule:** $$\text{Mass of one molecule} = \frac{78.97}{6.022 \times 10^{23}} = 1.311 \times 10^{-22} \text{ g}$$ 6. **Interpretation:** The mass of one molecule of PO3 is approximately $1.311 \times 10^{-22}$ grams.