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Which of the following contains the highest number of molecules?

1. 15 liters of hydrogen gas at STP
2. 5 liters of nitrogen gas at STP
3. 0.5 grams of hydrogen gas
4. 10 grams of oxygen gas

Correct answer: 15 liters of hydrogen gas at STP

Solution

Moles: 15 L H2 at STP = 0.67 mol; 5 L N2 = 0.22 mol; 0.5 g H2 = 0.25 mol; 10 g O2 = 0.31 mol. The 15 L H2 has the most molecules, so the correct option is index 0, not 2.

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