a)
$2NaCl+{{H}_{2}}S{{O}_{4}}\xrightarrow{\ge 400{}^\circ C}N{{a}_{2}}S{{O}_{4}}+2HCl$
$\begin{align}
& 4HCl+Mn{{O}_{2}}\xrightarrow{t{}^\circ }C{{l}_{2}}+MnC{{l}_{2}}+2{{H}_{2}}O \\
& C{{l}_{2}}+{{H}_{2}}O\to HCl+HClO \\
& HClO\to HCl+\frac{1}{2}{{O}_{2}} \\
& NaCl+AgN{{O}_{3}}\to AgCl+NaN{{O}_{3}} \\
& AgCl\xrightarrow{t{}^\circ }Ag+\frac{1}{2}C{{l}_{2}} \\
& Cu+C{{l}_{2}}\to CuC{{l}_{2}} \\
& CuC{{l}_{2}}r+{{H}_{2}}S{{O}_{4}}\to CuS{{O}_{4}}+2HCl \\
\end{align}$
b)
$\begin{align}
& 2KMn{{O}_{4}}+16HCl\to 5C{{l}_{2}}+2MnC{{l}_{2}}+2KCl+8{{H}_{2}}O \\
& C{{l}_{2}}+Cu\to CuC{{l}_{2}} \\
& Fe+CuC{{l}_{2}}\to FeC{{l}_{2}}+Cu \\
& 2FeC{{l}_{2}}+4{{H}_{2}}S{{O}_{4}}\to F{{e}_{2}}{{(S{{O}_{4}})}_{3}}+4HCl+S{{O}_{2}}+{{H}_{2}}O \\
& C{{l}_{2}}+{{H}_{2}}\to 2HCl \\
& CaC{{O}_{3}}+2HCl\to CaC{{l}_{2}}+C{{O}_{2}}+{{H}_{2}}O \\
& CaC{{l}_{2}}+2KOH\to Ca{{(OH)}_{2}}+2KCl \\
\end{align}$
c)
$\begin{align}
& 2KClr+{{H}_{2}}S{{O}_{4}}\to {{K}_{2}}S{{O}_{4}}+2HCl \\
& 4HCl+Mn{{O}_{2}}\to MnC{{l}_{2}}+C{{l}_{2}}+2{{H}_{2}}O \\
& C{{l}_{2}}+2NaBr\to 2NaCl+B{{r}_{2}} \\
& B{{r}_{2}}+2NaI\to 2NaBr+{{I}_{2}} \\
& Fe+C{{l}_{2}}\to FeC{{l}_{3}} \\
& FeC{{l}_{3}}+3AgN{{O}_{3}}\to 3AgCl+Fe{{(N{{O}_{3}})}_{3}} \\
& 2AgCl+Cu\to CuC{{l}_{2}}+2Ag \\
\end{align}$