Which of the following compounds has the greatest molar solubility in water?
a) HgS Ksp = 1.6 × 10⁻54
b) PbS Ksp = 7.0 × 10⁻29
c) CdS Ksp = 1.0 × 10⁻28
d) FeS Ksp = 3.7 × 10⁻18