Barium chloride is used estimate sulphur content in the molecule. In Carius tube test, a known mass of sulphur present in an organic compound with Silver Nitrate is heated into a sealed tube known as Carius tube with silver. The organic compound is then converted to Sulphuric acid which then reacts with excess Barium Chloride solution and produces a precipitate of Barium Sulphate. Z is BaSO4 and Y is H2SO4
It is clear that " X " must contain sulphur. Methionine is C5H11NO2S, a sulphur contaning amino acid