Consider a buffer made of acetic acid CH₃COOH and its conjugate base CH₃COONa with a pH of 4.60. If Ka of CH₃COOH is 1.8 × 10⁻⁵, what is the concentration of CH₃COOH?
a) 0.0012 M
b) 0.0025 M
c) 0.0034 M
d) 0.0048 M