a,
$C+ O_2 \buildrel{{t^o}}\over\longrightarrow CO_2$
$CO_2+ Ca(OH)_2 \rightarrow CaCO_3+ H_2O$
$CaCO_3 \buildrel{{t^o}}\over\longrightarrow CaO+ CO_2$
$CaO+ H_2O \rightarrow Ca(OH)_2$
b,
$MnO_2+ 4HCl \rightarrow MnCl_2+ Cl_2+ 2H_2O$
$Cl_2+ H_2 \buildrel{{as}}\over\longrightarrow 2HCl$
$NaOH+ HCl \rightarrow NaCl+ H_2O$
$2NaCl \buildrel{{đpnc}}\over\longrightarrow 2Na+ Cl_2$
$2Fe+ 3Cl_2 \buildrel{{t^o}}\over\longrightarrow 2FeCl_3$
$FeCl_3+ 3KOH \rightarrow Fe(OH)3+ 3KCl$
$2Fe(OH)_3 \buildrel{{t^o}}\over\longrightarrow Fe_2O_3+ 3H_2O$