The chemical used for leaching of silver and gold is:

The correct answer is Option (1) → NaCN

Leaching is the concentration of an ore by dissolving the metal in a suitable reagent, leaving the impurities behind. In the metallurgy of silver and gold, the metal is leached with a dilute solution of NaCN (or KCN) in the presence of air (\( \ce{O2} \)). The metal forms a soluble cyanido complex:

The metal is then recovered from the solution by displacement with zinc, a more reactive metal.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Other Examples – “In the metallurgy of silver and that of gold, the respective metal is leached with a dilute solution of NaCN or KCN in the presence of air (for O₂) from which the metal is obtained later by replacement:
\( \ce{4M(s) + 8CN^-(aq) + 2H2O(aq) + O2(g) -> 4[M(CN)2]^-(aq) + 4OH^-(aq)} \) (M = Ag or Au)
\( \ce{2[M(CN)2]^-(aq) + Zn(s) -> [Zn(CN)4]^2-(aq) + 2M(s)} \)”