A gas mixture contains 50 mol% H2 and 50 mol% He. 1.00-L samples of this gas mixture are mixed with — Stoichiometry Chemistry Question

A gas mixture contains 50 mol% H₂ and 50 mol% He. 1.00-L samples of this gas mixture are mixed with variable volumes of O₂ (at 0 °C and 1 atm). A spark is introduced to allow the mixture to undergo complete combustion. The final volume is measured at 0 °C and 1 atm. Which graph best depicts the final volume as a function of the volume of added O2?