Calculate the amont of `SeO_(4)^(2-)` in solution on the basic of the following data. `20mL` of `M//60` solution of `KBrO_(3)` was added to a define volume of `SeO_(3)^(2-)` solution. The bromic evolved was removed by boiling and excess of `KBrO_(3)` was back titrated with `5.1mL` of `M//25` solution fo `NaAsO_(2)`. The reaction are given below:
(a) `SeO_(3)^(2-) + BrO_(3)^(-) + H^(+) rarr SeO_(4)^(2-) + Br_(2) + H_(2)O`
(b) `BrO_(3)^(-) + AsO_(2)^(-) + H_(2) O rarr Br^(-) + AsO_(4)^(3-) + H^(+)`

Answer

`0.084g`