A metallic nitrate `(A)` on strong heating leaves behind a residue along with liberation of gases. The metallic nitrate on treatment with `H_(2)S//H^(+)` gives a black precipitate `(B)^(-)` insoluble in hot dilute nitric acid, but the precipitate dissolves in aquaregia.
Which of the following observation is true ? If the metallic nitrate is dissolved in `H_(2)O` and then treated with `NH_(3)`

Options

A. forms a black precipitated of HgO
B. forms a soluble complex `[Hg(NH_(3))_(-2)]^(2+)`
C. forms a black precipitate of mixed composition
D. forms a white precipitate of mixed composition.

Answer

D

Explanation

`underset((A))(Hg(NO_(3))_(2))rarrHg+NO_(2)+O_(2)`
`darrH_(2)S//H^(+)`
`underset((B))(HgS)`
`Hg(NO_(3))_(2)+NH_(3)+H_(2)OrarrHgO`
`Hg(NH_(2))NO_(3)darr+NH_(4)^(+)`( White ppt of mixed composition)