A black mineral (A) on heating in presence of air gives a gas (B). The mineral (A) on reaction with dilute `H_(2)SO_(4)` gives a gas (C) and a solution of a compound (D) on passing the gas (C) into an aqueous solution of (B), a white turbidity is obtained. The aqueous solution of (D) on reaction with potassium ferricyanide gives a blue compound (E). Identify (A) to (E) and give chemical equations for the reaction involved.