Gold can be dissolved from gold-bearing rock by treating the rock with sodium cyanide in the presence of oxygen.

(a) Name the oxidizing and reducing agents in this reaction. What has been oxidized, and what has been reduced?

(b) If you have exactly one metric ton (1 metric ton = 1000 kg) of gold-bearing rock, what volume of 0.075 M NaCN, in liters, do you need to extract the gold if the rock is 0.019% gold?

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4 Au(s) + 8 NaCN(aq) + O₂(g) + 2 H₂O(l) → 4 NaAu(CN)₂(aq) + 4 NaOH(aq)