Final answer:
The suitable materials for use as electrodes in aqueous electrolytic cells are platinum (Pt) and graphite because they are inert and electrically conductive. The correct answer is C. Pt and graphite only.
Step-by-step explanation:
The question asked is about the suitability of various substances to be used as electrodes in electrolytic cells containing aqueous solutions. In such cells, electrodes should be electrically conductive and inert in the environment of the electrolyte.
Sodium (Na) would react vigorously with water, and sulfur (S) is a non-metal and not conductive enough for use as an electrode. Mercury (Hg) electrodes are not typically used in standard aqueous solutions due to potential toxicity and its liquid state at room temperature.
Therefore, the suitable substances from the given options that can be used as electrodes in aqueous solutions are platinum (Pt) and graphite. These materials are inert and electrically conductive, allowing them to serve as effective pathways for electron transfer without reacting with the electrolyte or the products of electrolysis.
The correct answer to the question is C. Pt and graphite only.