\(\begin{array}{l}
a)\\
2Na + 2{H_2}O \to 2NaOH + {H_2}\\
N{a_2}O + {H_2}O \to 2NaOH\\
2NaCl + 2{H_2}O \to 2NaOH + C{l_2} + {H_2}\\
Ba{(OH)_2} + N{a_2}S{O_4} \to 2NaOH + BaS{O_4}\\
b)\\
Cu + C{l_2} \to CuC{l_2}\\
Cu + 2FeC{l_3} \to 2FeC{l_2} + CuC{l_2}\\
CuO + 2HCl \to CuC{l_2} + {H_2}O\\
CuS + 2HCl \to CuC{l_2} + {H_2}S
\end{array}\)