`HgCl_(2)` and `I_(2)` both when dissolved in water containing `I^(-)` ions the pair of species formed is:

Options

A. `HgI_(2), I^(-)`
B. `HgI_(4)^(2-), I_(3)^(-)`
C. `Hg_(2)I_(2), I^(-)`
D. `HgI_(2), I_(3)^(-)`

Answer

B

Explanation

In a solution containing `HgCl_(2),I_(2)` and `I^(-)`, both `HgCl_(2)` and `I_(2)` complete for `I^(-)`.
Since formation constant constant of `[HgI_(4)]^(-2)` is `1.9 xx 10^(30)` which is very large as compared with `I_(3)^(-) (k_(f) = 700)`
Therefore, `I^(-)` will perferentially combine with `HgC1_(2)`
`HgCI_(2) +2I^(-) underset("Soluble complex")underset([HgI_(4)]^(-2))underset(darr+2I^(-))(HgI_(2) +2CI^(-))`
`I_(2) + I^(-) rarr I_(3)^(-)`
water soluble