Which of the following anions cannot be easily removed from its aqueous solution by precipitation?

$AgNO_3$ gives a red precipitate with:

Which anion of a sodium salt gives a white precipitate upon heating with a magnesium salt?

Which of the following anions cannot be tested by $dil. H_2SO_4$?

In the chromyl chloride test,the reagent used is

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: