An queous solution of a substance gives a white precipitate on treating with dilute hydrochloric acid which dissolves on heating. When hydrogen sulphide is passed through the hot solution, a black precipitate is obtained. The substance is :

Options

A. `Hg^(2+)` salt
B. `Cr^(3+)` salt
C. `Ag^(+)` salt
D. `Pb^(2+)` salt

Answer

A

Explanation

`Hg^(2+)` salt gives white precipitate with dilute HCl.
`HgO + 2HCl rarr underset(("White ppt"))(HgCl_(2)) + H_(2)O`
`HgCl_(2) + H_(2)S rarr underset(("Black ppt"))(HgS) + 2HCl`