Three test tubes, `A,B,C,` contain `Pb^(2+),Hg_(2)^(2+)` and `Ag^(+)` ( but unknown ) . To each aqueous solution, `NaOH` is added is excess . Following changes occur.
`A :` Black p p t, `B:` Brown ppt `, C :` White ppt but dssolves in excess of `NaOH`
`A,B` and `C` contain respectively.

Options

A. `Pb^(2+),Hg_(2)^(2+), Ag^(+)`
B. `Hg_(2)^(2+),Ag^(+),Pb^(2+)`
C. `Ag^(+),Pb^(2+),Hg^(2+)`
D. `Ag^(+),H_(2)^(2+),Pb_(2)^(2+)`

Answer

B

Explanation

`Ha_(2)^(2+)+2NaOHrarrH_(2)Odarr("black")+2Na^(+)+H_(2)O`
`2A^(+)+2NaOHrarrAg_(2)Odarr("brown but turns black when dried")+2Na^(+)+H_(2)O`
`Pb^(2+)+4NaOHrarrNa_(2)PbO_(2)("soluble")+2Na^(+)+2H_(2)O`