Đáp án C
$Zn,Cu,Fe,Cr\xrightarrow{{{O}_{2}},HCl}$$ZnC{{l}_{2}},CuC{{l}_{2}},FeC{{l}_{3}},CrC{{l}_{3}}$ $\xrightarrow{N{{H}_{3}}}\left\{ \begin{align}
& Fe{{\left( OH \right)}_{3}},Cr{{\left( OH \right)}_{3}}\xrightarrow{{{t}^{o}}}F{{e}_{2}}{{O}_{3}},C{{r}_{2}}{{O}_{3}} \\
& Zn{{\left( N{{H}_{3}} \right)}_{4}}{{\left( OH \right)}_{2}},Cu{{\left( N{{H}_{3}} \right)}_{4}}{{\left( OH \right)}_{2}} \\
\end{align} \right.$