When the lead-acid cell is fully charged, the electrolyte assumes _____ appearance

The correct answer is: C. bright

When a lead-acid cell is fully charged, the electrolyte assumes a bright appearance. This is because the electrolyte is a solution of sulfuric acid, which is a clear, colorless liquid. When the cell is fully charged, the sulfuric acid is in a state of equilibrium, and there is no excess of either sulfuric acid or water. This results in a clear, bright appearance of the electrolyte.

The other options are incorrect because they do not accurately describe the appearance of the electrolyte when a lead-acid cell is fully charged.

• Option A is incorrect because a dull appearance is not characteristic of a fully charged lead-acid cell.
• Option B is incorrect because a reddish appearance is characteristic of a lead-acid cell that is not fully charged.
• Option D is incorrect because a milky appearance is characteristic of a lead-acid cell that is damaged or has been overcharged.