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# $H_2S$ in the presence of HCl precipitates group II but not group IV because

(a) HCl activates $H_2S$
(b) HCl increases the concentration of $Cl^-$ ions
(c) HCl decreases the concentration of $S^{2-}$ ions
(d) HCl lowers the solubility of $H_2S$ in the solution

Answer: HCl decreases the concentration of $S^{2-}$ ions

Due to common ion effect, HCl suppresses the ionisation of $H_2S$ thus decreasing the concentration of $S^{2-}$ ions. Only group II radicals are precipitated.