An unknown contains one or more of Pb²⁺, Hg₂²⁺, and Ag⁺. It forms a white precipitate with HCl(aq). The precipitate is treated with hot water, yielding a solution that gives a yellow precipitate with K₂CrO₄(aq). There is no change in color when the undissolved portion of the precipitate is treated with NH₃(aq). Indicate for each chloride group cation whether it is present or absent, or about which there is some doubt.