A white solid dissolves in water to form a neutral solution. No precipitate forms when this olution is treated with a solution of NH4CL/NH3 buffer, nor when (NH4)2S is added. When the solution is acidified with HC2H3O2 and K2CrO4 is added, a yellow precipitate forms. This precipitate dissolves upon addition of concentrated HCL. Acidification of a solution of the solid with HNO3 followed by addition of AgNO3 causes formation of a white precipitate. What is the identity of the original solid?