Chemistry - Coordination Chemistry Question with Solution | TestHub

Reaction (A): Cu²⁺ in CuSO₄ reacts with excess KCN to form $[Cu(CN{)}_4]$³⁻, where Copper is reduced to Cu⁺.

Reaction (D): Gold (Au) in alluvial sand (oxidation state 0) reacts with NaCN and O₂ (Air) to form $[Au(CN{)}_2]$⁻, where Gold is oxidized to Au⁺.

In contrast, reactions (B) and (C) involve ligand substitution or complex formation without a change in the metal's oxidation state (Cu²⁺ and Ag⁺ remain unchanged).