Which of the following salts shows the lowest solubility in water? (Kₛₚ values: Ag₂S = 1.6 × 10⁻⁴⁹, Bi₂S₃ = 1.0 × 10⁻⁷², HgS = 1.6 × 10⁻⁵⁴, Mg(OH)₂ = 8.9 × 10⁻¹², MnS = 2.3 × 10⁻¹³
a) Ag₂S
b) Bi₂S₃
c) HgS
d) Mg(OH)₂