1. **State the problem:** We need to calculate the density of oxygen gas given its mass and volume. 2. **Recall the formula for density:** $$\text{density} = \frac{\text{mass}}{\text{volume}}$$ 3. **Convert mass to grams:** Given mass is 2.23 kg. Since 1 kg = 1000 g, $$2.23\ \text{kg} = 2.23 \times 1000 = 2230\ \text{g}$$ 4. **Use the given volume:** Volume is already in cm³: $$1.56 \times 10^{6}\ \text{cm}^3$$ 5. **Calculate density:** $$\text{density} = \frac{2230}{1.56 \times 10^{6}}$$ 6. **Perform the division:** $$\text{density} = 1.429487179 \times 10^{-3}$$ 7. **Express in standard form to 3 significant figures:** $$\text{density} = 1.43 \times 10^{-3}\ \text{g/cm}^3$$ **Final answer:** The density of the oxygen gas is $$1.43 \times 10^{-3}\ \text{g/cm}^3$$.