Upon treatment with ammoniacal H2S, the metal ion that precipitates as a sulfide is: Fe(III), Zn(II), Mg(II), Al(III)

Upon treatment with ammonical H2S, the metal ion that precipitates as a sulfide is Zn(II). The chemical equation for this is as follows:
Zn(II) + H2S(ammonical) → ZnS + 2H
As, NH4OH + H2S gas, is the group reagent for the Zn(II) ion. So, only this can give the precipitate with ammonical H2S.