On passing H2S gas through a solution of Cu+ and Zn+2 ions, CuS is precipitated first because: (i) Solubility product of CuS is equal to the ionic product of ZnS (ii) Solubility product of CuS is equal to the solubility product of ZnS (iii) Solubility product of CuS is lower than the solubility product of ZnS (iv) Solubility product of CuS is greater than the solubility product of ZnS.
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