1. **State the problem:** Find the mass of 3 L of hydrogen gas at 300°C and pressure $2 \times 10^{4}$ Pa, with molar mass $M=2$ g/mol and gas constant $R=8.314$ J/(mol·K). The temperature in Kelvin is now $T=300+273=573$ K (without the 0.15). 2. **Use the ideal gas law:** $$PV = nRT$$ where $P$ is pressure, $V$ is volume, $n$ is number of moles, $R$ is gas constant, and $T$ is temperature. 3. **Convert volume to cubic meters:** $$V = 3\,L = 3 \times 10^{-3}\,m^{3}$$ 4. **Calculate number of moles $n$:** $$n = \frac{PV}{RT} = \frac{(2 \times 10^{4})(3 \times 10^{-3})}{8.314 \times 573}$$ 5. **Calculate numerator:** $$2 \times 10^{4} \times 3 \times 10^{-3} = 60$$ 6. **Calculate denominator:** $$8.314 \times 573 \approx 4764.822$$ 7. **Calculate moles:** $$n = \frac{60}{4764.822} \approx 0.01259\,mol$$ 8. **Calculate mass:** $$m = n \times M = 0.01259 \times 2 = 0.02518\,g$$ **Final answer:** The mass of hydrogen is approximately $0.0252$ grams.