Paragraph: An aqueous solution of a mixture of two inorganic salts,...

Paragraph: An aqueous solution of a mixture of two inorganic salts, when treated with dilute $H C$ ?, gave a precipitate $(\boldsymbol{P})$ and a filtrate $(\boldsymbol{Q})$. The precipitate $\boldsymbol{P}$ was found to dissolve in hot water. The filtrate $(\boldsymbol{Q})$ remained unchanged, when treated with $\mathrm{H}_{2} \mathrm{~S}$ in a dilute mineral acid medium. However, it gave a precipitate $(\boldsymbol{R})$ with $H_{2} S$ in an ammoniacal medium. The precipitate $\boldsymbol{R}$ gave a coloured solution $(\boldsymbol{S})$, when treated with $\mathrm{H}_{2} \mathrm{O}_{2}$ in an aqueous $\mathrm{NaOH}$ medium.
Question: The coloured solution $\boldsymbol{S}$ contains