Colourless KI solution turned brown.

Note: If more aq. KI is added, black deposits of I₂ crystals are formed.

Redox reaction.

Solution P has oxidised colourless KI solution to brown iodine solution. Iodide ions lose electrons to become oxidised to iodine molecules.

2I^- (aq)    ----->     I₂ (aq) + 2e^-

Solution P is an oxidizing agent.

Redox reaction.

Solution Q has oxidised colourless KI solution to brown iodine solution. Iodide ions lose electrons to become oxidised to iodine molecules.

2I^- (aq)    ----->     I₂ (aq) + 2e^-

Solution Q is an oxidizing agent. It contains copper(II) ions that are reduced to copper(I) ion and combines with iodide ions to form insoluble copper(I) iodide which appears to be a grey ppt. in the brown iodine solution.

2Cu²⁺ (aq)+ 4I^- (aq)    ----->    2CuI (s)    +    I₂ (aq)
                                           copper(I) iodide