At 25 °C the molar solubility of a sparingly soluble salt AB₂ is 3.0×10⁻³ mol L⁻¹. When the solution is heated, the molar solubility exactly doubles. By what factor does the value of Ksp for AB₂ change over this temperature range?
a) 4
b) 2
c) 8
d) 16