$X_2S_n + H_2O \to X(OH)_n \downarrow + Y \uparrow (Gas) \xrightarrow{Pb(CH_3COO)_2} Z \downarrow (Black \ ppt.)$
Then $(X)$ cation can not be

Which compound does not dissolve in hot dilute $HNO_3$?

The only cations present in a slightly acidic solution are $Fe^{3+}$,$Zn^{2+}$,and $Cu^{2+}$. The reagent that when added in excess to this solution would identify and separate $Fe^{3+}$ in one step is

When $MgSO_4$ reacts with $NH_4OH$ and $Na_2HPO_4$,it forms a white crystalline substance. What is the formula of that substance?

Compound $A$ on borax bead test in reducing flame gives green colour bead. Compound $A$ on treatment with $H_2O_2$ followed by treatment with $Pb(OAc)_2$ gives yellow ppt. The metal ion in the compound $A$ is :

$A$ reagent used to test the presence of $Fe^{2+}$ ion is