A 0.085 M solution of phenylacetic acid (C₆H₅CH₂COOH) has a pH of 2.68. Calculate the Kₐ for this acid.
a) 1.0 × 10-4
b) 2.0 × 10-3
c) 3.0 × 10-5
d) 4.0 × 10-6