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Which of the following steps in metallurgy requires oxygen?

1. Calcination of dolomite
2. Roasting of cinnabar
3. Zone refining of Si
4. Leaching of gold by NaCN solution

Correct answer: Roasting of cinnabar

Solution

Roasting of cinnabar (HgS) requires oxygen to convert the sulfide ore to oxide; calcination involves thermal decomposition without air, zone refining is a physical purification, and leaching uses a chemical solution.

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