You are looking at extracting a pyridine-bearing compound (conjugate acid pKa = 4) from an organic phase and transfer it to the aqueous phase. Which of the following aqueous solutions can you use to do so?
a. NaOH (pH = 13)
b. HCl (pH = 1)
c. NH₄OH (pH = 9)
d. KOH (pH = 11)