A compound (A) when treated with Kl gives a Scarlet red ppt. (B) which dissolves in excess of Kl. This solution is made alkaline with NaOH and gave brown precipitate (C) when `NH_(3)` gas is passed through it. When (A) is added with small amount of `SnCl_(2)` it gives a white ppt (D) but gives grey precipitate with excess amount of `SnCl_(2)`. When `H_(2)S` gas is passed through an acidic solution of (A) a black precipitate (E) is obtained. Identify (A) to (E). Write the reactions involved.

Explanation

`A=HgCl_(2)" "B=Hgl_(2)`

`D=Hg_(2)Cl_(2)" "E=H_(2)S`
Reaction are
`underset((A))(HgCl_(2))+2Kl rarr underset("(Scarlet ppt)")(Hgl_(2))+underset((B))(2KCl`
`Hgl_(2)+underset("(Excess)")(2Kl) rarr underset("(Soluble)")(K_(2)Hgl_(4))`

`underset((A))(2HgCl_(2)+SnCl_(2) rarr SnCl_(4)+underset("White (D)")(Hg_(2)Cl_(2))`
`Hg_(2)Cl_(2)+underset("(Excess)")(SnCl_(2))rarr SnCl_(4)+underset("(grey)")(2Hg)`
`HgCl_(2)+H_(2)S rarr underset("(E) black ppt")(HgS)+2HCl`