0.2 millimoles of ${\mathrm{Zn}}^{2+}$ ion is mixed with${\left({\mathrm{NH}}_4\right)}_2$ S of molarity 0.02 M. The amount of ${\mathrm{Zn}}^{2+}$ that remains unprecipitated in 20 mL of this solution would be : (Given: ${\mathrm{K}}_{\mathrm{sp}}$ (ZnS) = 4 x 10- 24 )