The correct option is Carbon on heating.
Explanation
The method used for extracting a metal from its ore depends on the metal's position in the reactivity series. Metals in the middle of the reactivity series, such as zinc, iron, and lead, are moderately reactive. These metals are typically extracted by reducing their oxides using a suitable reducing agent, most commonly carbon.
Detailed Analysis:
- Carbon on heating (Correct): Zinc oxide ($ZnO$) is reduced to metallic zinc ($Zn$) by heating with carbon (often in the form of coke). Carbon acts as a reducing agent, removing oxygen from the metal oxide to form carbon monoxide. The chemical reaction is:
$ZnO(s) + C(s) \xrightarrow{\text{Heat}} Zn(s) + CO(g)$ - Nitric acid (Incorrect): Nitric acid ($HNO_3$) is a strong oxidizing agent. It is typically used to dissolve metals or form salts (nitrates) rather than to reduce metal oxides.
- Hydrogen peroxide (Incorrect): Hydrogen peroxide ($H_2O_2$) functions primarily as a strong oxidizing agent. It is not used as a reducing agent in metallurgical extraction processes.
- Sodium chloride (Incorrect): Sodium chloride ($NaCl$) is a stable salt. It does not possess the chemical properties required to act as a reducing agent for metal oxides.
Key Takeaway: Carbon is the primary reducing agent used in the smelting process to extract moderately reactive metals (like Zinc, Iron, and Lead) from their respective oxides.