Which of the following ions form precipitates when $H_2S$ gas is passed through an acidic mixture containing $Cu^{2+}, Ni^{2+},$ and $Zn^{2+}$?

Statement-$1$: Few drops of $HNO_3$ are added before proceeding to $III^{rd}$ group.
Statement-$2$: For the oxidation of $Fe^{+2} \rightarrow Fe^{+3}$.

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

In the group $III$ radicals,in place of $NH_4Cl$,which of the following can be used?

Three separate samples of a solution of a single salt gave these test results: one formed a white precipitate with excess ammonia solution,one formed a white precipitate with dilute $NaCl$ solution,and one formed a black precipitate with $H_2S$. The salt could be:

When $H_2S$ is passed through a solution in $Group-II$ analysis,it sometimes becomes milky. This indicates the presence of: