Calculate the Minimum Concentration of Cr³⁺ That Must Be Added

Calculate the minimum concentration of Cr³⁺ that must be added to 0.095 M NaF in order to initiate a precipitate of chromium(III) fluoride.[K_sp(CrF₃) = 6.6 × 10^-11]

A) 0.023 M
B) 0.032 M
C) 7.7 × 10^-8 M
D) 2.9 × 10^-9 M
E) 6.9 × 10^-10 M