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Compound G
This is a white powder which gives a lilac flame colour. On heating the solid melts and gives off a gas which relights a glowing splint. A solution of the residue from heating gives a pale yellow precipitate with acidified silver nitrate solution. This precipitate is insoluble in concentrated ammonia solution.
The lilac flame test suggests a potassium salt. The gas which relights a glowing splint is oxygen. The production of oxygen on heating suggests a group 1 nitrate (other than lithium) or a halate. The silver nitrate test indicates that the residue is probably an iodide, but possibly a bromide. The insolubility in ammonia confirms an iodide. This suggests that the original compound was an iodate.
Answer: potassium iodate(V) or potassium iodate(VII).