Giải thích các bước giải:

\[\left\{ \begin{array}{l} CuO\\ Cu\\ Al\\ A{l_2}{O_3} \end{array} \right.\xrightarrow{+Cl_2\ \text{du}}\left\langle \begin{array}{l} \left\{ \begin{array}{l} CuO\\ A{l_2}{O_3} \end{array} \right.\xrightarrow{+NaOH\ \rm{du}} \left\langle \begin{array}{l} CuO\\ \left\{ \begin{array}{l} NaOH\;{\rm{du}}\\ NaAl{O_2} \end{array} \right.\xrightarrow{+CO_2\ \rm{du}}\downarrow Al(OH)_3\xrightarrow{t^\circ}Al_2O_3 \end{array} \right.\\ \left\{ \begin{array}{l} CuC{l_2}\\ AlC{l_3} \end{array} \right.\xrightarrow{+NaOH\ \text{du}} \left\langle \begin{array}{l} Cu{(OH)_2}\xrightarrow{t^\circ} CuO\xrightarrow{+H_2\ \rm{du}} Cu\\ \left\{ \begin{array}{l} NaOH\;{\rm{du}}\\ NaAl{O_2} \end{array} \right. \xrightarrow{+CO_2\ \rm{du}} \downarrow Al(OH)_3\xrightarrow{+HCl\ \rm{du,\ co\ can}}AlCl_3\xrightarrow{dpdd}Al \end{array} \right. \end{array} \right.\]