An aqueous solution of a mixture of two inorganic salts, when treated with dilute HCl, gave a precipitate (P) and a filtrate (Q). The precipitate P was found to dissolve in hot water. The filtrate (Q) remained unchanged , when treated with $H_{2}S$ in a dilute mineral acid medium. However, it gave a precipitate (R) with $H_{2}S$ in an ammoniacal medium. The precipitate R gave a coloured solution (S), when treated with $H_2{O}_2$ in an aqueous NaOH medium.
The precipitate P contains

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