A white crystalline salt imparts a violet colour to a Bunsen flame, and with hot concentrated H2SO4 , forms a pungent gas. On treatment with an AgNO3 solution, this gas forms a white precipitate readily soluble in NH3 . The white crystalline salt may be
(A) Na2SO4
(B) KCl
(C) CaCl2
(D) SrCl2