Acidic ferric chloride solution on treatment with excess of potassium ferrocyanide gives a Prussian blue coloured colloidal species. It is :

Which one of the following complexes is violet in colour?

To an aqueous solution containing ions such as Al³⁺, Zn²⁺, Ca²⁺, Fe³⁺, Ni²⁺, Ba²⁺ and Cu²⁺ was added conc. HCl, followed by H₂S.

The total number of cations precipitated during this reaction is/are :

When silver nitrate solution is added to potassium iodide solution then the sol produced is :