An unknown compound burns with a lilac flame and produces a yellow precipitate when mixed with dilute nitric acid and silver nitrate. Give the formula of the compound.

(Talk about needing to memorise colour tests for base metals and tests for Halides) The compound is KI (potassium Iodide) because potassium compounds burn with a lilac flame, and production a pale yellow precipitate show the formation of Iodide ions. *(mention ammonia test to see if the precipitate dissolves, which it won't to distinguish from Bromide)