Difficult ACT Science Problem?

<p>For some reason, this has been the only problem that I've encountered and haven't been able to figure out. I literally spent at least 20 minutes looking at it, and I can't seem to figure out how to find the answer, which is D. Maybe I'm just missing something small? I don't know, but if anyone can tell me how to solve it, I would greatly appreciate it. Thanks!
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<p>From the trials, we see that 2 mol (or liters) of H react with one mol (or liter) O to produce H2O. If we react 50 L H with 50 L O, we expect 25 L H2O and 25 L unreacted oxygen, so the answer is J.</p>

<p>Limiting reagent chemistry problem. Answer is J. Google for explanations</p>