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Consider the extraction of silver from argentite (Ag2S) ore by the cyanide process. Which of the following statements is correct?
- NaCN acts as a depressant
- Zn acts as a reducing agent
- NaOH acts as the leaching agent
- Zn produces [Zn(CN)4]²- complex
Correct answer: Zn acts as a reducing agent
Solution
In the cyanide process, Ag2S is leached with dilute NaCN in the presence of air to form the soluble complex [Ag(CN)2]⁻. Silver is then recovered by adding Zn metal, which displaces Ag (Zn is oxidized, reducing Ag⁺ to Ag⁰). The by-product is [Zn(CN)4]²-. Hence 'Zn acts as a reducing agent' is the correct and precise statement.
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