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 HAsO₄²⁻ 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 these choices are correct.