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From the list Na, Hg, S, Pt and graphite, which substances are suitable for use as electrodes in the electrolysis of aqueous solutions?

1. Hg and Pt
2. Hg, Pt and graphite
3. Na, S
4. Na, Hg, S

Correct answer: Hg, Pt and graphite

Solution

Na reacts violently with water, so it cannot serve as an electrode in aqueous solution. Sulphur is a non-metal and a poor electrical conductor, so it is unsuitable. Mercury (a liquid metal, used as a cathode in the chlor-alkali Hg-cell), platinum (an inert noble metal), and graphite (a conducting, inert non-metal) all conduct and are chemically stable enough to act as electrodes in aqueous electrolysis.

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