Give the pH of 0.330 M phosphoric acid. For phosphoric acid, Ka1 = 7.5 x 10^-3, Ka2 = 6.2 x 10^-8, and Ka3 = 4.2 x 10^-13 .
A. 3.84
B. 6.43
C. 2.61
D. 5.68
E. 1.30