Question

the solubility of pbBr2 0.012m a) 25°c caculate the ksp

Answer 1

You should learn to be more precise. I assume you meant 0.012 M and not 0.012 m. M stands for molarity; m stands for molality.

....................PbBr2 ==> Pb^2+ + 2Br^-
I.....................solid...........0.............0
C.....................-x..............x.............2x
E....................solid...........x.............2x
Ksp = (Pb^2+)(Br^-)^2 = (x)(2x)^2 =?
The problem tells you that x = 0.012 M. Substitute and solve for Ksp.