The cation that will not be precipitated by H₂S in the presence of dil HCl is: Pb²⁺, As³⁺, Cu²⁺, Co²⁺

Co²⁺ will not be precipitated by H₂S in the presence of dil HCl as dil HCl will suppress the ionization of H₂S. To affect the precipitation, H₂S should be used in the ammoniacal solution.