A Solution Contains [Ba²⁺] = 5

Multiple Choice

A solution contains [Ba²⁺] = 5.0 × 10^-5 M, [Ag⁺] = 3.0 × 10^-5 M, and [Zn²⁺] = 2.0 × 10^-7 M. Sodium oxalate is slowly added so that [C₂O₄^2-] increases.
What is the concentration of the first cation to precipitate when the second cation just begins to precipitate?

A) 1.3 × 10^-6
B) 2.2 × 10^-6
C) 5.0 × 10^-5
D) 1.35 × 10^-9
E) 1.1 × 10^-11