A sample of pure water is saturated with PbCl2. In this saturated solution, which of the following is true?
a. Ksp = [Pb²⁺]2[Cl⁻]
b. Ksp = [Pb²⁺][Cl⁻]
c. [Pb²⁺] = 0.5[Cl⁻]
d. [Pb²⁺] = [Cl⁻]