Reagents used for the qualitative estimation of $Ni^{+2}$ and $Cu^{+2}$ respectively are:

$A$ mixture of $NaCl$ and $K_{2}Cr_{2}O_{7}$ is heated with conc. $H_{2}SO_{4}$,deep red vapours are formed. Which of the following statements is false?

Which one among the following pairs of ions cannot be separated by $H_2S$ in dilute hydrochloric acid?

$Al^{3+}$,$Fe^{3+}$,$Zn^{2+}$,and $Ni^{2+}$ ions are present in an acidic solution. Excess of ammonium chloride $(NH_4Cl)$ solution is added followed by the addition of ammonium hydroxide $(NH_4OH)$ solution. The resulting precipitate will contain:

Precipitate of group $IV$ cations takes place when $H_2S$ is

Which compound gives a black color with $NH_4OH$?