Ksp=[Pb][Cl]²
since we know that for every atom of Pb in solution, there are 2 atoms of Cl. That means if we set [Pb]=x, [Cl]=2x and we can rewrite the Ksp equation as Ksp=x4x² and then you can solve for x to find the [Pb] in the solution. Since there is 1 mole of Pb in 1 mol of PbCl₂, and the units of molarity is moles/L, we can say that the concentration of Pb in the solution is equal to the solubility of PbCl₂.
7.3x10^12=4x³
x³=1.825x10^12
x=12220M
Therefore the solubility of PbCl₂ is 12220 moles/liter
This works since Ksp is referring to the maximum amount of solute that can dissolve in the solution and is therefore directly related to how soluble a compound is. The bigger the Ksp is , the more soluble it is.
I hope this helps.
