Which of the following statements about gold (Au) element are correct?
(A) Gold occurs in nature in native state.
(B) Gold dissolves in aqua-regia.
(C) Gold is extracted by leaching the metal with dilute NaCN.
(D) Leaching is followed by replacement reaction.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (B), (C) and (D)
(A) Gold occurs in nature in native state — True. Gold is a noble metal and is found free (native), for example in quartz veins and river sands.
(B) Gold dissolves in aqua-regia — True. Aqua regia (3 HCl : 1 \( \ce{HNO3} \)) oxidises Au and the \( \ce{Cl^{-}} \) ions hold it as \( \ce{[AuCl4]^{-}} \).
(C) Gold is extracted by leaching the metal with dilute NaCN — True. In the presence of air, gold dissolves as the soluble complex \( \ce{[Au(CN)2]^{-}} \).
(D) Leaching is followed by replacement reaction — True. Zinc, a more reactive metal, displaces gold from the complex:
\( \ce{2[Au(CN)2]^- (aq) + Zn(s) -> 2Au(s) + [Zn(CN)4]^{2-} (aq)} \)
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):
Leaching – “… 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.”
Oxidation Reduction – “… As studied earlier, extraction of gold and silver involves leaching the metal with CN–. This is also an oxidation reaction (Ag → Ag+ or Au → Au+). The metal is later recovered by displacement method.”
\( \ce{4Au(s) + 8CN^-(aq) + 2H2O(aq) + O2(g) -> 4[Au(CN)2]^-(aq) + 4OH^-(aq)} \)
\( \ce{2[Au(CN)2]^-(aq) + Zn(s) -> 2Au(s) + [Zn(CN)4]^2-(aq)} \)
“In this reaction zinc acts as a reducing agent.”