Appearance of blood red colour, on treatment of the sodium fusion extract of an organic compound with $$\mathrm{FeSO}_4$$ in presence of concentrated $$\mathrm{H}_2 \mathrm{SO}_4$$ indicates the presence of element/s

In the wet tests for detection of various cations by precipitation, $$\mathrm{Ba}^{2+}$$ cations are detected by obtaining precipitate of

When a solution of mixture having two inorganic salts was treated with freshly prepared ferrous sulphate in acidic medium, a dark brown ring was formed whereas on treatment with neutral $$\mathrm{FeCl}_{3}$$, it gave deep red colour which disppeared on boiling and a brown red ppt was formed. The mixture contains :

Formation of which complex, among the following, is not a confirmatory test of $$\mathrm{Pb}^{2+}$$ ions :