Arsenic Acid, H₃AsO₄, Is Used Industrially to Manufacture Insecticides

Arsenic acid, H₃AsO₄, is used industrially to manufacture insecticides. Arsenic acid is a polyprotic acid with K₁ = 2.5 × 10^-4, K₂ = 5.6 × 10^-8, and K₃ = 3 × 10^-13. What is the concentration of the HAsO₄^2- in a solution whose initial arsenic acid concentration was 0.35 M?

A) 9.4 × 10^-3 M
B) 2.5 × 10^-4 M
C) 8.8 × 10^-5 M
D) 5.6 × 10^-8 M
E) none of the above