The Acid-Dissociation Constants of Phosphoric Acid (H₃PO₄)are K_a1 = 7

The acid-dissociation constants of phosphoric acid (H₃PO₄) are K_a1 = 7.5 × 10^-3, K_a2 = 6.2 × 10^-8, and K_a3 = 4.2 × 10^-13 at 25.0 °C. What is the pH of a 2.5 M aqueous solution of phosphoric acid?

A) 1.82
B) 0.40
C) 2.51
D) 0.86
E) 0.13