Question

calculate the minimum concentration of ag+ ion that must be added to (or built up in) a 0.140 m Na2CrO4 solution in order to initiate a precipitation of silver chromate. The ksp of ag2cro4 is 1.2 × 10^-12.

Answer 1

I will assume you have writer's cramp and you can't use the caps key. Sentences begin with a capital letter, you know, and it's important that you remember that m stands for molality and M stands for molarity. There's a difference. So that must be 0.140 M. Also, ag2cro4 means nothing to me especially when you realize CO stands for carbon monoxide, Co stands for cobalt, and co stands for company.
Ag2CrO4 ==> 2Ag^2+ + CrO4^2-

Ksp = (Ag^2+)^2(CrO4^2-)
You know CrO4^2-, plug in and solve for Ag^+.