Answer: C. Each metal + dilute HCl gives \(\text{H}_2\) gas. With excess acid, the gas volume produced is determined by the moles of metal used, scaled by the number of \(\text{H}_2\) molecules released per metal atom.
For Mg (\(M_r = 24\)): \(\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\). Moles \(\text{Mg}\) = \(1.0/24 = 0.0417\); moles \(\text{H}_2\) = 0.0417.
For Ca (\(M_r = 40\)): moles \(\text{H}_2\) = \(1.0/40 = 0.0250\).
For Zn (\(M_r = 65\)): moles \(\text{H}_2\) = 0.0154.
For Fe (\(M_r = 56\), gives \(\text{FeCl}_2 + \text{H}_2\)): moles \(\text{H}_2\) = 0.0179.
Magnesium has the lowest \(M_r\) per H₂ produced, so 1.0 g gives the most gas — C.
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