A student electrolysed sodium sulfate solution using inert electrodes. The volume of gas collected at each electrode was measured every minute. Figure shows the results.
Figure: Volume of gas collected at each electrode against time during the electrolysis of sodium sulfate solution

Use Figure to determine the volume of gas collected at the negative electrode after 4 minutes.
Name the gas collected at the negative electrode.
Use Figure to describe how the volume of gas collected at the positive electrode compares with the volume collected at the negative electrode.
Explain why oxygen, and not sulfur, is produced at the positive electrode.
40 exam-style questions on AQA GCSE Chemistry 4.3 Electrolysis, covering 4.3.1a The process of electrolysis, 4.3.1b Half equations in electrolysis, 4.3.2 Electrolysis of molten ionic compounds, 4.3.3 Using electrolysis to extract metals, 4.3.4 Electrolysis of aqueous solutions, and 4.3.5 Representation of reactions at electrodes as half equations. Each one has a worked solution and a mark scheme showing where the marks go.