What Is the Approximate Concentration of Free Ni²⁺ Remaining at Equilibrium

Multiple Choice

What is the approximate concentration of free Ni²⁺ remaining at equilibrium in a solution prepared by mixing 5.0 mL of 0.10 M NiCl₂ with 5.0 mL of 2.0 M NH₃(aq) ? [The net formation constant for the hexamminenickel(II) ion is 5.5 × 10⁸.]

A) 1.8 × 10^-9 M
B) 7.7 × 10^-10 M
C) 1.3 × 10^-10 M
D) 2.4 × 10^-10 M
E) 0.050 M