During the electrolytic refining of copper, precious metals like gold and silver collect at the bottom of the anode as:
Correct: C
In the electrolytic refining of copper, the impure copper forms the anode. As copper dissolves from the anode, more reactive metals also dissolve into the electrolyte. However, less reactive metals, such as gold, silver, and platinum, do not dissolve in the electrolyte and fall off the anode to collect at the bottom as 'anode sludge' (also called anode mud). This sludge is a valuable source of these precious metals.