To an aqueous solution containing ions such as $Al^{3+}, Zn^{2+}, Ca^{2+}, Fe^{3+}, Ni^{2+}, Ba^{2+}$ and $Cu^{2+}$,concentrated $HCl$ was added,followed by $H_{2}S$. The total number of cations precipitated during this reaction is/are:

On addition of aqueous $NaOH$ to a salt solution,a white gelatinous precipitate is formed,which dissolves in excess alkali. The salt solution contains

Passing $H_2S$ gas into a mixture of $Mn^{2+}$,$Ni^{2+}$,$Cu^{2+}$ and $Hg^{2+}$ ions in an acidified aqueous solution precipitates

Nessler's reagent is

$A$ salt reacts with dilute $HCl$ to produce a gas with a pungent smell and yellow crystals. When tested,the salt gives a green flame. With potassium chromate,the salt gives yellow crystals. Therefore,the salt is.......

Addition of sodium thiosulphate solution to a solution of silver nitrate gives $X$ as a white precipitate, which is insoluble in water but soluble in excess thiosulphate solution to give $Y$. On boiling in water, $Y$ gives $Z$. $X$, $Y$, and $Z$ respectively are: