The formation constant for the metal–EDTA complex (where EDTA is indicated by the symbol Y) can be expressed for the net equilibrium reaction as:

Mn+ + Y4– ⇌ (MY)n–4 with Kf = [(MY)n-4]/[Mn+][Y4–]

Based upon this information only, which one of the following metal cations present in the same mixture would you expect to react with EDTA first?

Calcium (Ca2+), Kf=10.7

Cerium (Ce3+), Kf = 15.9

Lead (Pb2+), Kf = 18.0

Zinc (Zn2+), Kf = 16.7