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In the electrolytic purification of copper, certain impurity metals do not dissolve and collect at the bottom as anode sludge. Which of the following metals are found in that sludge?

1. Fe and Ni
2. Ag and Au
3. Pb and Zn
4. Sn and Ag

Correct answer: Ag and Au

Solution

Silver and gold are less reactive and do not dissolve in the electrolytic process, causing them to accumulate as anode sludge during copper purification.

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