When a solution of mixture of two inorganic salts was treated with freshly prepared ferrous sulphate in acidic medium, a dark brown ring was formed whereas on treatment with neutral FeCl$$_3$$, it gave deep red colour which disappeared on boiling and a brown red ppt was formed. The mixture contains

We need to identify the two anions based on the given tests:

Test 1: Brown ring test

When treated with freshly prepared ferrous sulphate in acidic medium, a dark brown ring was formed. This is the characteristic brown ring test for nitrate (NO$$_3^-$$) ions.

$$\text{NO}_3^- + 3\text{Fe}^{2+} + 4\text{H}^+ \rightarrow 3\text{Fe}^{3+} + \text{NO} + 2\text{H}_2\text{O}$$

$$[\text{Fe(H}_2\text{O)}_5\text{NO}]^{2+}$$ gives the brown ring.

Test 2: Neutral FeCl$$_3$$ test

Treatment with neutral FeCl$$_3$$ gave a deep red colour which disappeared on boiling and a brown-red precipitate was formed. This is the characteristic test for acetate (CH$$_3$$COO$$^-$$) ions.

$$3\text{CH}_3\text{COO}^- + \text{Fe}^{3+} \rightarrow (\text{CH}_3\text{COO})_3\text{Fe}$$

The deep red colour is due to ferric acetate. On boiling, it hydrolyses to form a brown-red precipitate of basic ferric acetate.

Therefore, the mixture contains CH$$_3$$COO$$^-$$ and NO$$_3^-$$.