An aqueous solution contains an unknown concentration of `Ba^(2+)`. When 50 mL of a 1 M solution of `Na_(2)SO_(4)` is added, `BaSO_(4 )`just begins to precipitate. The final volume is 500 mL. The solubility product of `BaSO_(4)` is `1xx10^(–10)`. What is the original concentration of `Ba^(2+)`?
A. `1.0xx10^(-10)M`
B. `5xx10^(-9)M`
C. `2xx10^(-9)M`
D. `1.1xx10^(-9)M`
