Calculate the total volume of residual gases after the reaction between 60 cm³ of H₂ and 20 cm³ of O₂ at 100°C.

To determine the total volume of residual gases, we first write the balanced chemical equation for the reaction between hydrogen and oxygen: Step 1: Write the balanced chemical equation. The reaction of hydrogen gas with oxygen gas produces water. Since the temperature is 100^, water will be in its gaseous state (steam). 2H_2(g) + O_2(g) 2H_2O(g) Step 2: Determine the limiting reactant. According to Gay-Lussac's Law of Combining Volumes, at constant temperature and pressure, the volumes of gaseous reactants and products are in simple whole-number ratios corresponding to the stoichiometric coefficients in the balanced equation. From the equation, 2 volumes of H_2 react with 1 volume of O_2. Given volumes: Volume of H_2 = 60 cm^3 Volume of O_2 = 20 cm^3 To react completely with 20 cm^3 of O_2, the required volume of H_2 would be: 2 × 20 cm^3 = 40 cm^3 of H_2 Since we have 60 cm^3 of H_2, which is more than the 40 cm^3 required, oxygen (O_2) is the limiting reactant. Step 3: Calculate the volumes of reactants consumed and products formed. Oxygen consumed: All 20 cm^3 of O_2 will be consumed. Hydrogen consumed: Based on the 2:1 ratio with O_2, 2 × 20 cm^3 = 40 cm^3 of H_2 will be consumed. Water vapor formed: Based on the 2:2 (or 1:1) ratio with O_2, 2 × 20 cm^3 = 40 cm^3 of H_2O(g) will be formed. Step 4: Calculate the volume of residual gases. Unreacted hydrogen: Initial H_2 - Consumed H_2 = 60 cm^3 - 40 cm^3 = 20 cm^3. Unreacted oxygen: 0 cm^3 (all consumed). Water vapor (product): 40 cm^3. The residual gases are the unreacted hydrogen and the water vapor formed. Step 5: Calculate the total volume of residual gases. Total volume of residual gases = Volume of unreacted H_2 + Volume of H_2O(g) Total volume of residual gases = 20 cm^3 + 40 cm^3 = 60 cm^3. The total volume of the residual gases is 60 cm^3. The final answer is A. 60 cm^3.