In the refinement of gold a basic solution of Au(CN)4- is electrolyzed. Gold metal and oxygen gas are produced at the electrodes. Answer the following questions by selecting the appropriate reaction.

Which half-reaction takes place at the anode during this electrolysis?
4OH- --> O2 + 2H2O + 4e-
Au(CN)4- + 3e- --> Au + 4CN-
H2O2 --> O2 + 2H+ + 2e-
Au + 4CN- --> Au(CN)4- + 3e-

Which is the overall cell reaction for this electrolysis?
2Au(CN)4- + 6OH- + 3H2 --> 2Au + 8CN- + 6H2O
4Au(CN)4- + 6H2O --> 4Au + 16CN- + 3O2 + 12H+
4Au(CN)4- + 12OH- --> 4Au + 16CN- + 3O2 + 6H2O
4Au + 16CN- + 3O2 + 6H2O --> 4Au(CN)4- + 12OH-

Which half-reaction takes place at the cathode during this electrolysis?
Au + 4CN- --> Au(CN)4- + 3e-
Au(CN)4- + 3e- --> Au + 4CN-
4OH- --> O2 + 2H2O + 4e-
O2 + 2H2O + 4e- --> 4OH-

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