When $H_2S$ gas is passed through a solution,it reacts to form a white precipitate. Which ion is present in the solution?

An inorganic compound $X$ on treatment with concentrated $H_{2}SO_{4}$ produces brown fumes and gives a dark brown ring with $FeSO_{4}$ in the presence of concentrated $H_{2}SO_{4}$. Also,compound $X$ gives a precipitate $Y$ when its solution in dilute $HCl$ is treated with $H_{2}S$ gas. The precipitate $Y$ on treatment with concentrated $HNO_{3}$ followed by excess of $NH_{4}OH$ further gives a deep blue coloured solution. Compound $X$ is:

Among the following cations,the number of cations which will give characteristic precipitate in their identification tests with $K_4[Fe(CN)_6]$ is :
$Cu^{2+}, Fe^{3+}, Ba^{2+}, Ca^{2+}, NH_4^{+}, Mg^{2+}, Zn^{2+}$

Which compound gives a black color with $NH_4OH$?

Which of the following ions forms a colored carbonate precipitate?

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