Passing H2S gas into a mixture of Mn2+, Ni2+, Cu2+ and Hg2+ ions in an acidified aqueous solution precipitates:

H2S in presence of aqueous acidified solution precipitates as sulphide of Cu and Hg as CuS and HgS. But the solubility product of Mn2+, Ni2+ are higher thus they remain unaffected. Hence, the correct option is A.