Chemistry - Salt Analysis Question with Solution | TestHub

The Cu²⁺ ion is reduced to the Cu⁺ state by reagents that are moderate reducing agents or those that form stable Cu(I) complexes:

Option (A) KI₍aq₎: Iodide ions (I⁻) reduce Cu²⁺ to a white precipitate of CuI (where Cu is +1) while being oxidized to I₂.

Option (D) KCN₍aq₎: Cyanide ions (CN⁻) reduce Cu²⁺ to Cu⁺, eventually forming the stable soluble complex $[Cu(CN{)}_4]$³⁻.

Option (B) is incorrect because metallic Zn is a strong reducing agent that typically reduces Cu²⁺ all the way to metallic copper (Cu⁰).

Option (C) is incorrect because K₂Cr₂O₇ is a powerful oxidizing agent, not a reducing agent.