Suppose You Are Studying Coordination Compounds of Co(II) with the Ligand

Suppose you are studying coordination compounds of Co(II) with the ligand pyridine (py, C₅H₅N, molar mass = 79.10) . You isolate a crystalline compound, and because the only available anions are Cl^- and NO₃^-, you hypothesize that the empirical formula of the coordination compound must be Co_w(py) _x(Cl) _y(NO₃) _z.
-You analyze for pyridine (K_b is approximately 10^-9) by dissolving 0.1000 g of the complex in 100 mL of H₂O and titrating with a 0.01 M HCl solution. Which of the following indicators should be used to detect the endpoint? (Assume that the initial concentration of pyridine is approximately 0.01 M.)

A) thymol blue, pH range of color change = 8.0-9.6
B) methyl red, pH range of color change = 4.8-6.0
C) bromophenol blue, pH range of color change = 3.0-4.6
D) bromothymol blue, pH range of color change = 6.0-7.6
E) alizarin yellow, pH range of color change = 10.1-12.0