Magnesium is a chemical element with symbol Mg. It is found in various salts like magnesium chloride and magnesium sulphate as Mg2+ ion. In group VI, magnesium ions form a precipitate of magnesium ammonium phosphate with ammonium phosphate solution. Magnesium ions react with ammonium phosphate in presence of ammonium chloride and ammonium hydroxide to form white precipitate of magnesium ammonium phosphate.
This video explains how to test for the presence of magnesium ion in a given salt.