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Compound E
This is a white crystalline solid. On warming with dilute sodium hydroxide solution a gas is evolved which turn damp red litmus blue. Treatment with silver nitrate solution gives a white precipitate which is insoluble in dilute acid but which is readily soluble in dilute ammonia solution.
The only common alkaline gas found at "A" level is ammonia. This means the original substance must have been an ammonium salt. The silver nitrate test shows the presence of a chloride.
Answer: ammonium chloride.
We could have confirmed ammonia gas by looking for white fumes with hydrogen chloride gas. The use of ammonia confirms the presence of a chloride. The similarity of the colours for silver chloride and silver bromide can lead to confusion. Further evidence for ammonium chloride can be obtained by checking for sublimation of the solid.