A certain compound (A) is used in the laboratory for analysis, its aqueous solution gives the following reactions:
a. On addition to copper sulphate, a brown precipitate is obtained which turns white on addition of excess of the `Na_(2)S_(2)O_(3)` solution.
b. On addition to the `Ag^(o+)` ion solution, a yellow curdy precipitate is obtained which is insoluble in ammonium hydroxide. Identify (A) and give equations for the reactions at steps (a) and (b).

Explanation

`X - KI`
`2CuSO_(4)+2KI rarr 2CuI_(2)+K_(2)SO_(4)`
`2CuI_(2) rarr underset("white")(Cu_(2)I_(2))+I_(2)`
`I_(2)+2Na_(2)S_(2)O_(3) rarr Na_(2)S_(4)O_(6)+2 NaI`