a. $Al \to AlC{l_3} \to Al{\left( {OH} \right)_3} \to A{l_2}{O_3} \to Al$
$2Al+3Cl_2 → 2AlCl_3$
$AlCl_3+3NaOH → Al(OH)_3+3NaCl$
$2Al(OH)_3 → Al_2O_3+3H_2O$
$2A{l_2}{O_3}\xrightarrow{{dpnc}}4Al + 3{O_2}$
b. $NaCl \to NaOH \to N{a_2}C{O_3} \to N{a_2}S{O_4} \to NaCl \to C{l_2} \to AlC{l_3} \to Al{\left( {OH} \right)_3} \to A{l_2}{O_3} \to Al \to NaAl{O_2}$
$2NaCl + 2{H_2}O\xrightarrow[{cmn}]{{dp{\text{dd}}}}2NaOH + C{l_2} + 2{H_2}$
$2NaOH+CO_2 → Na_2CO_3+H_2O$
$Na_2CO_3+H_2SO_4 → Na_2SO_4+H_2O+CO_2$
$Na_2SO_4+BaCl_2 → BaSO_4+2NaCl$
$2NaCl\xrightarrow{{dpnc}}2Na + C{l_2}$
$3Cl_2+2Al → 2AlCl_3$
$AlCl_3+3NaOH → Al(OH)_3+3NaCl$
$2Al{\left( {OH} \right)_3}\xrightarrow{{{t^0}}}A{l_2}{O_3} + 3{H_2}O$
$2A{l_2}{O_3}\xrightarrow{{dpnc}}4Al + 3{O_2}$
$2Al+2NaOH+2H_2O → 2NaAlO_2+3H_2$
c. $Fe{S_2} \to S{O_2} \to S{O_3} \to {H_2}S{O_4} \to CuS{O_4} \to N{a_2}S{O_4} \to NaOH \to N{a_2}Zn{O_2}$
$4FeS_2+11O_2 → 2Fe_2O_3+8SO_2$
$2SO_2+O_2 → 2SO_3$
$SO_3+H_2O → H_2SO_4$
$H_2SO_4+Cu(OH)_2 → CuSO_4+2H_2O$
$CuSO_4+2NaOH → Cu(OH)_2+Na_2SO_4$
$Na_2SO_4+Ba(OH)_2 → 2NaOH+BaSO_4$
$2NaOH+Zn → Na_2ZnO_2+H_2$
d. $Mg \to MgS{O_4} \to Mg{\left( {OH} \right)_2} \to MgO{\text{ }} \to MgC{l_2} \to Mg{\left( {N{O_3}} \right)_2} \to MgC{O_3} \to MgO$
$Mg+H_2SO_4 → MgSO_4+H_2$
$MgSO_4+Ba(OH)_2 → Mg(OH)_2+BaSO_4$
$Mg(OH)_2 → MgO+H_2O$
$MgO+2HCl → MgCl_2+H_2O$
$MgCl_2+2AgNO_3 → Mg(NO_3)_2+2AgCl$
$Mg(NO_3)_2+Na_2CO_3 → 2NaNO_3+MgCO_3$
$MgC{O_3}\xrightarrow{{{t^o}}}MgO + C{O_2}$
