Ammonium ion is a positively charged polyatomic ion with formula NH4+. It is formed by the protonation of ammonia. It has tetrahedral structure. Ammonium ion is found in variety of salts such as ammonium carbonate, ammonium chloride and ammonium nitrate. When ammonium salt is heated with conc. NaOH, ammonia gas is evolved which gives white fumes of ammonium chloride with dil.HCl and a brown coloured precipitate with Nessler’s reagent.
This video explains how to test the presence of ammonium ion in a given salt.