Chemistry · Qualitative Inorganic Analysis

When an aqueous solution containing a mixture of two inorganic salts was treated with freshly prepared ferrous sulphate solution in the presence of concentrated sulphuric acid, a dark brown ring was formed at the junction. On the other hand, treatment of the original mixture solution with neutral FeCl3 gave a deep red colouration, which disappeared on boiling to form a brown-red precipitate. The mixture contains which of the following pairs of anions?