Consider a Solution Made by Mixing 500

Consider a solution made by mixing 500.0 mL of 4.0 M NH₃ and 500.0 mL of 0.40 M AgNO₃. Ag⁺ reacts with NH₃ to form AgNH₃⁺ and Ag(NH₃) ₂⁺: The concentration of Ag(NH₃) ₂⁺ at equilibrium is

A) 0.20 M.
B) 2.0 M.
C) 0.40 M.
D) 1.0 * 10^-3 M.
E) none of these