An apple green colour in the flame test indicates the presence of Ba2+ ion.
The group precipitate of Ba2+ is BaCO3, which dissolves in acetic acid to form barium acetate. Upon treatment with K2CrO4, it gives a yellow precipitate of barium chromate (BaCrO4), confirming the presence of Ba2+.
When the sodium carbonate extract is heated with conc. HNO3 and ammonium molybdate, the formation of a canary yellow precipitate indicates the presence of phosphate (PO43−) ion. The canary yellow precipitate is ammonium phosphomolybdate, (NH4)3PO4⋅12MoO3.
Therefore, the cation is Ba2+ and the anion is PO43−.
Answer: Ba2+ and PO43−