In the cyanide process for extraction of gold and silver from ores, the cyanide solution acts as a:

When gold and silver are extracted from ores using the cyanide method, the cyanide solution serves as a leaching agent, bringing the metals into the solution as cyanide complexes and separating them from the ore.

Cyanide is used in the extraction of silver and gold (Mac Arthur - Forrest process). Following initial crushing and concentration by froth flotation, the ore is leached using a diluted (0.4–7%) solution of sodium cyanide made alkaline by adding lime and maintained stirred by an air current. Silver (or gold) dissolves as argentocyanide in the solution.

It is based on the observation that silver and gold dissolve in a dilute solution of sodium cyanide in the presence of oxygen from the atmosphere, forming complex cyanide.

The following reaction is obtained,

${\mathrm{Ag}}_2\mathrm{S}+4\mathrm{NaCN}\to 2\mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN}{)}_2\right]+{\mathrm{Na}}_2\mathrm{S}$

Silver is produced by a reaction with zinc:

$2\mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN}{)}_2\right]+\mathrm{Zn}\to {\mathrm{Na}}_2\left[\mathrm{Zn}(\mathrm{CN}{)}_4\right]+2\mathrm{Ag}$

Hence Correct option is B.