Answer: C. At the same temperature and pressure, equal moles of any gas occupy equal volumes (Avogadro's law). The smallest volume corresponds to the smallest number of moles.
Compute moles using \(n = \dfrac{\text{mass}}{M_r}\):
A: 4 g of \(\text{H}_2\) (\(M_r = 2\)) → \(n = 2\) mol.
B: 34 g of \(\text{NH}_3\) (\(M_r = 17\)) → \(n = 2\) mol.
C: 44 g of \(\text{CO}_2\) (\(M_r = 44\)) → \(n = 1\) mol.
D: 48 g of \(\text{O}_2\) (\(M_r = 32\)) → \(n = 1.5\) mol.
The smallest mole count is C (1 mol), so 44 g of carbon dioxide occupies the smallest volume.
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