Which gas occupies the highest volume at STP?

At the same temperature and pressure, gas volume is proportional to the number of moles (Avogadro’s law). The samples contain 0.02, 0.1, 1, and 2 moles, respectively, so 2 mol of H₂ occupies the greatest volume. Therefore, the correct choice is D, 2 mol of H₂.

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