First write the dissociation reaction for Ag2CrO4.
Then find relationship between concentration of ions and solubility product.
Now do the calculation to find the concentration of [CrO4]2−.
Let the solubility of Ag2CrO4=xmol/LAg2CrO4→2Ag+CrO42− ions 2xx ∴Ksp=[Ag+]2[CrO4−2]=(2x)2(x)
or Ksp=4x3 or x=34Ksp
Given, Ksp=3432×10−2 =38×10−12=2×10−4mol/L