An aqueous solution contains an unknown concentration of $\mathrm{B}{\mathrm{a}}^{2+}$ . When 50 mL of a 1 M solution of $\mathrm{N}{\mathrm{a}}_2\mathrm{S}{\mathrm{O}}_4$ is added $\mathrm{B}\mathrm{a}\mathrm{S}{\mathrm{O}}_4$ just begins to precipitate. The final volume is 500 mL. The solubility product of $\mathrm{B}\mathrm{a}\mathrm{S}{\mathrm{O}}_4$ is $1\times 10^{-10}$ . What is the original concentration of $\mathrm{B}{\mathrm{a}}^{2+}$ ?

• A

  $1.0\times 10^{-10}\mathrm{M}$
• B

  $5\times 10^{-9}\mathrm{M}$
• C

  $2\times 10^{-9}\mathrm{M}$
• Correct answer
  D

  $1.1\times 10^{-9}\mathrm{M}$

Hence, the correct answer is option: 'D'.