Step 1: Understand the matching task. We must pair each metallurgy step in List A with the right process in List B. Knowing what each ore and metal needs makes the matching easy.
Step 2: Match the sulphide ore (A). Separating a sulphide ore like ZnS from rocky impurities is done by Froth Floatation, because sulphide particles cling to oil and froth and float up. So A goes with Froth Floatation (II).
Step 3: Match the bauxite step (B). Purifying bauxite ($Al_2O_3$) to remove impurities is done by Leaching, where a chemical dissolves the alumina selectively. So B goes with Leaching (I).
Step 4: Match the gold recovery (C). Getting gold out of its leached solution by adding zinc is a Displacement reaction, since the more reactive zinc pushes out the less reactive gold. So C goes with Displacement (IV).
Step 5: Match the zinc extraction (D). Getting zinc metal from ZnO needs removal of oxygen, which is Reduction (using carbon). So D goes with Reduction (III).
Step 6: Combine the pairs. Putting them together gives A-II, B-I, C-IV, D-III. \[ \boxed{\text{A-II, B-I, C-IV, D-III}} \]
