Calculate the Molar Concentration of Uncomplexed Zn²⁺ in a Solution $\times$

Multiple Choice

Calculate the molar concentration of uncomplexed Zn²⁺ in a solution that contains 0.20 mole of Zn(NH₃) ₄²⁺ per liter and 0.0116 M NH₃ at equilibrium.The overall K_f for Zn(NH₃) ₄²⁺ is 3.8 $\times$ 10⁹.

A) 2.9 $\times$ 10^-3 M
B) 8.8 $\times$ 10^-3 M
C) 6.7 $\times$ 10^-4 M
D) 2.0 $\times$ 10^-13 M
E) none of these