Answer: B. First estimate the volume of gas. \(n(\text{Mg}) = 0.19 / 24 \approx 7.9 \times 10^{-3}\,\text{mol}\), and Mg + 2HCl → MgCl₂ + H₂ gives the same number of moles of hydrogen, so \(V(\text{H}_2) \approx 7.9 \times 10^{-3} \times 24\,000 \approx 190\,\text{cm}^3\) at room temperature and pressure.
To follow the rate of reaction you must measure this volume at intervals. A 50 cm³ gas syringe (A) and a 50 cm³ inverted burette (C) are far too small — about 190 cm³ of hydrogen would overshoot them. Measuring the loss in mass on a balance (D) is impractical because hydrogen is so light that the mass change is tiny. An inverted 250 cm³ measuring cylinder filled with water (B) collects the gas by displacement and lets you read off the volume at each time.
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