Which of the following metals can be extracted through alkali leaching technique?

<p>The alkali leaching technique is a method to extract metals from their ores by using an alkaline solution, typically a sodium hydroxide (NaOH) solution, sometimes in the presence of other substances like a cyanide for gold and silver ores. Among the options given, the metal that can be extracted through alkali leaching technique is:</p> <p>Option C: $\mathrm{Au}$ (Gold)</p> <p>Gold can be extracted using a process known as cyanidation or cyanide leaching. In this process, finely ground gold-bearing ore is treated with a dilute solution of sodium cyanide (NaCN) or potassium cyanide (KCN) in the presence of oxygen to dissolve the gold. The chemical reaction for the dissolution of gold in the cyanide solution is given by:</p> $\mathrm{4Au + 8NaCN + O_2 + 2H_2O \rightarrow 4Na[Au(CN)_2] + 4NaOH}$ <p>The gold is then recovered from the solution by various methods, such as adsorption onto activated carbon, followed by elution and eventually electro-winning or by precipitation with zinc dust (the Merrill-Crowe process). Because of environmental and safety concerns, alternatives to cyanide leaching have been researched, yet cyanidation remains the primary method for the recovery of gold from its ores.</p> <p>As for the other options:</p> <p>Option A: $\mathrm{Sn}$ (Tin) is generally extracted through pyrometallurgical processes such as smelting, rather than alkali leaching.</p> <p>Option B: Copper (Cu) is often extracted using hydrometallurgical processes like sulfuric acid leaching rather than alkali leaching. Copper can also be extracted using the process called solvent extraction and electrowinning (SX-EW) after the leaching step.</p> <p>Option D: $\mathrm{Pb}$ (Lead) is typically extracted using pyrometallurgical methods, including smelting and refining, and not alkali leaching.</p>