Science (086) — CBSE Class 10 board question

(i) Extraction of Zn from ZnS:

Step 1 – Roasting (ZnS converted to ZnO):

$$2\text{ZnS} + 3\text{O}_2 \xrightarrow{\Delta} 2\text{ZnO} + 2\text{SO}_2$$

Step 2 – Reduction (ZnO reduced by coke):

$$2\text{ZnO} + \text{C} \xrightarrow{\Delta} 2\text{Zn} + \text{CO}_2$$

(ii) Nitric acid is a strong oxidising agent. It oxidises the hydrogen gas produced during the reaction to water (H₂O). Therefore, hydrogen gas is not evolved; instead, oxides of nitrogen (like NO, NO₂) are released.

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• For (i), the two-step process — roasting followed by reduction — must be shown as separate balanced equations. Both steps carry marks; missing either loses a mark.
• For (ii), the key phrase is oxidising agent: HNO₃ oxidises H₂ to H₂O before it can escape, so NO/NO₂ is evolved instead. Always mention this in one clear sentence.