The triprotic acid H3X has pKa1=2.1, pKa2=7.5, and pKa3=12.0. In a particular solution, 85\% of the species are HX2− and 15\% are X3−, with all other forms negligible. Which pH value or range is most consistent with these data?
a) pH≈12.0 (equal to pKa3)
b) pH≈12.8 (slightly above pKa3)
c) pH≈11.2 (slightly below pKa3)
d) pH≈10.3 (well below pKa3)