Solubility
product constants are values to describe the saturation of ionic compounds with
low solubility. A saturated solution is when there is a dynamic equilibrium
between the solute dissolved, the dissociated ions, the undissolved and the
compound. It is calculated from the product of the ion concentration in the
solution. For the base, Ca(OH)2, the dissociation would be as
follows:
Ca(OH)2 = Ca2+ + 2OH-
So, the expression for the solubility product constant would be as follows:
Ksp = [Ca2+] [OH-]^2
let x be the concentration of the Ca2+. So,
Ksp = [x] [2x]^2
Ksp = 4x^3
You have to substitute the value of the concentration of the calcium hydroxide in the final expression which is not given in the problem statement in order to evaluate Ksp.