Q.At a site, low grade copper ores are available and zinc and iron scraps are also available. Which of the two scraps would be more suitable for reducing the leached copper ore and why?

Leached low-grade copper ore gives a $Cu^{2+}$ solution. Any metal higher than copper in the electrochemical series can displace it, e.g. $Fe + Cu^{2+} \rightarrow Fe^{2+} + Cu$ or $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$. Zinc, being more reactive, would displace copper somewhat more efficiently, but zinc scrap is costlier and has more competing industrial uses, whereas iron scrap is abundant and cheap — so iron is the industrially …

Step 1 – The chemistry: displacement from leach liquor

Low-grade copper ore is leached (with dilute acid or bacterial action) to bring copper into solution as $Cu^{2+}$ ions. Any metal more electropositive than copper (i.e., higher in the activation/electrochemical series) can then displace metallic copper from this solution:

Step 2 – Compare zinc and iron as the displacing scrap

Both zinc and iron lie above copper in the electrochemical series and can precipitate metallic copper from solution. Zinc is the more reactive of the two and would in principle displace copper slightly more readily/completely.

Step 3 – The deciding factor: economics, not chemistry …

Identify that both metals can displace copper via the electrochemical series, then weigh the practical/economic factor (cost, availability …

• Answering purely on reactivity ('zinc is more reactive, so use zinc') while ignoring the economic angle the question is actually testing. …