Which one of the following anions is not easily removed from aqueous solutions by precipitation?

When chlorine water is added to an aqueous solution of potassium halide in the presence of chloroform,a violet colour is obtained. On adding more chlorine water,the violet colour disappears,and a colourless solution is obtained. This test confirms the presence of which of the following in the aqueous solution?

Which ion's salt solution produces a violet layer when chlorine water and chloroform are added?

When a solution of a mixture having two inorganic salts was treated with freshly prepared ferrous sulphate in an acidic medium,a dark brown ring was formed,whereas on treatment with neutral $FeCl_3$,it gave a deep red colour which disappeared on boiling and a brown-red precipitate was formed. The mixture contains:

$P_{(Coloured \ Solution)} + BaCl_2 \to Q \downarrow_{(White)} + R_{(Coloured \ Solution)}$
Then salt $P$ in above reaction is

In a test tube containing a salt, a few drops of dilute $\text{H}_2\text{SO}_4$ were added, which gave colourless vapours having the smell of vinegar. The vapours turned the blue litmus paper red. Identify the correct anion from the following: