7404/1 Chemistry Jun 2023 Quiz | AQA AS Level MCQ

Magnesium reacts with an acid to form hydrogen gas.
Line X on the graph shows how the volume of hydrogen gas varies with time when 50 cm$^3$ of 0.50 mol dm$^{–3}$ acid reacts with an excess of magnesium.
The reaction is repeated under the same conditions but using 25 cm$^3$ of 1.50 mol d$m$^{–3}$ acid. The magnesium is in excess.
Which line represents…