What ([H₃O⁺]) must be maintained in a saturated (H₂S) solution to precipitate (Pb²⁺), but not (Zn²⁺) from a solution in which each ion is present at a concentration of 0.1 M?
a) (1 × 10⁻⁴ , M)
b) (5 × 10⁻⁵ , M)
c) (2 × 10⁻⁴ , M)
d) (1 × 10⁻⁵ , M)