Match List-I with List-II.
| List-I (Process) | List-II (Substance used) |
|---|---|
| (A) Estimation of hardness of water | (I) Zinc |
| (B) Separation of gold in metallic form from a solution of \( \ce{[Au(CN)2]^-} \) | (II) D-Penicillamine |
| (C) Smooth and even electroplating of articles with silver | (III) Na2EDTA |
| (D) Removal of copper present in toxic proportions in the body | (IV) \( \ce{[Ag(CN)2]^-} \) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-III, B-I, C-IV, D-II
Each of these processes depends on the formation of a coordination compound, or, for gold, on getting the metal back out of one.
(A) Estimation of hardness of water — This matches (III) Na2EDTA. Hard water is titrated with Na2EDTA; the Ca2+ and Mg2+ ions form stable complexes with EDTA.
(B) Separation of gold in metallic form from a solution of [Au(CN)2]− — This matches (I) Zinc. Gold first dissolves in cyanide (with oxygen and water) as [Au(CN)2]−; when zinc is added to this solution, gold separates in metallic form.
(C) Smooth and even electroplating of articles with silver — This matches (IV) [Ag(CN)2]−. Silver deposits much more smoothly and evenly from a solution of this complex than from a solution of simple Ag+ ions.
(D) Removal of copper present in toxic proportions in the body — This matches (II) D-Penicillamine. This is chelate therapy: the chelating ligand binds the excess copper as a coordination compound, which is then removed.
NCERT (2026-27 edition):
5.7 Importance and Applications of Coordination Compounds – “Hardness of water is estimated by simple titration with Na2EDTA. The Ca2+ and Mg2+ ions form stable complexes with EDTA.”
“Gold, for example, combines with cyanide in the presence of oxygen and water to form the coordination entity [Au(CN)2]– in aqueous solution. Gold can be separated in metallic form from this solution by the addition of zinc.”
“Articles can be electroplated with silver and gold much more smoothly and evenly from solutions of the complexes, [Ag(CN)2]– and [Au(CN)2]– than from a solution of simple metal ions.”
“…Thus, excess of copper and iron are removed by the chelating ligands D–penicillamine and desferrioxime B via the formation of coordination compounds.”