Extraction of silver from ${\mathrm{Ag}}_2\mathrm{S}$ by the use of sodium cyanide is an example of:

Extraction of silver from  ${\mathrm{Ag}}_2\mathrm{S}$ by the use of sodium cyanide is an example of hydrometallurgy. Hydrometallurgy involves pre-treatments such as leaching, impurity separation, and precipitation to recover metal or metal compounds from ore. When uranium, gold, silver, zinc, and copper are extracted from low-grade ores, it is utilized.

Hence, option B is correct