\(\begin{array}{l}
a)\\
{H_2}S + 4C{l_2} + 4{H_2}O \to 8HCl + {H_2}S{O_4}\\
2{H_2}S{O_4}(dn) + Cu \to CuS{O_4} + S{O_2} + 2{H_2}O\\
S{O_2} + 2NaOH \to N{a_2}S{O_3} + {H_2}O\\
N{a_2}S{O_3} + 2HCl \to 2NaCl + S{O_2} + {H_2}O\\
S{O_2} + B{r_2} + 2{H_2}O \to {H_2}S{O_4} + 2HBr\\
Zn + {H_2}S{O_4} \to ZnS{O_4} + {H_2}\\
b)\\
4Fe{S_2} + 11{O_2} \to 2F{e_2}{O_3} + 8S{O_2}\\
S{O_2} + B{r_2} + 2{H_2}O \to {H_2}S{O_4} + 2HBr\\
3Mg + 4{H_2}S{O_4} \to 3MgS{O_4} + S + 4{H_2}O\\
S + {O_2} \to S{O_2}\\
2S{O_2} + {O_2} \to 2S{O_3}\\
S{O_3} + {H_2}O \to {H_2}S{O_4}\\
Ba{(OH)_2} + {H_2}S{O_4} \to BaS{O_4} + 2{H_2}O
\end{array}\)