Which of the following radicals will not be precipitated by passing $H_2S$ in a concentrated acid solution?

The colour of the precipitate produced by adding $NaOH$ solution to $HgCl_2$ is

When a salt is treated with sodium hydroxide solution,it gives gas $X$. On passing gas $X$ through reagent $Y$,a brown-coloured precipitate is formed. $X$ and $Y$ respectively,are

Assign $A$,$B$,$C$,$D$ from the given type of reaction: $NiCl_2 (aq) + NaNO_3 (aq) \longrightarrow$ No reaction.

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

$A$ solution prepared in conc. $HCl$ sometimes gives white turbidity even in the absence of $1^{st}$ group,when water is added to it. It is due to the presence of