An inorganic compound 'A' is heat resistant. It gives a white precipitate when an aqueous solution of BaCl2 is added. It dissolves in dil HNO3 and when 'A' is heated with dil HCl, it produces the colourless gas X. That gas does not change the colour of KMnO4 solution. An aqueous solution of 'A' is used as a primary standard in titrations.
Further 'A' shows the following reactions.
A + Y(g) + H2O = B + X(g)
B + A = C + X(g) + H2O
C+ Sulphur = E
E gives a white precipitate first with AgNO3 and gradually changes the colour to black. Y decolourises acidified KMnO4 and is a gas. Identify B,C,X,Y.