Which of the following occupies the maximum volume at STP? [At. wt. C=12, O=16]

3 moles of hydrogen

Reason — At STP, 1 mole of any gas occupies 22.4 L.

• 3 moles of hydrogen = 3 × 22.4 = 67.2 L
• 1 mole of helium = 22.4 L
• 64 g of oxygen = $\frac{64}{32}$ = 2 moles = 44.8 L
• 44 g of carbon dioxide = $\frac{44}{44}$ = 1 mole = 22.4 L

Hence, 3 moles of hydrogen occupy the maximum volume (67.2 L).