The preferential discharge of ions during electrolysis is influenced by the

Analyze the question

The question asks which factor influences preferential (selective) discharge of ions during electrolysis. This is a standard topic in electrolysis.

Explain the concept

When an electrolyte contains more than one kind of ion, only one ion is usually discharged at each electrode. This is called preferential discharge. Three main factors control which ion is discharged:

1. Position of the ion in the electrochemical series. Ions lower in the series are discharged more easily.
2. Concentration of the ion in the electrolyte. A highly concentrated ion may be discharged in preference to one that is higher in ease of discharge. For example, in concentrated NaCl, Cl⁻ is discharged rather than OH⁻.
3. Nature of the electrode. For example, in CuSO₄(aq): • With inert (platinum or carbon) electrodes, OH⁻ is discharged at the anode, giving O₂. • With copper electrodes, the copper anode itself dissolves (Cu → Cu²⁺ + 2e⁻). Likewise, with a mercury cathode, Na⁺ is discharged in preference to H⁺.

Check the options

• A. Mechanism of electrolysis: not a recognized factor.
• B. Electrolytic reactions: these are the result of discharge, not a factor that influences it.
• C. Nature of the electrode: this is a recognized factor, as shown above.
• D. Type of electrolytic cell: not a factor; the cell type does not decide which ion is discharged.

Answer: The correct option is C, nature of the electrode.

Exam tip: Remember the three factors with "PCE": Position in the electrochemical series, Concentration, Electrode nature. If a WASSCE question asks about preferential discharge, look for one of these three.