a)
$2NaOH + CO_2\to Na_2CO_3 + H_2O$
$2NaOH + SO_2 \to Na_2SO_3 + H_2O$
$Ba(OH)_2 + CO_2 \to BaCO_3 + H_2O$
$Ba(OH)_2 + SO_2 \to BaSO_3 + H_2O$
b)
$NaOH + HCl \to NaCl + H_2O$
$NaOH + HNO_3 \to NaNO_3 + H_2O$
$Mg(OH)_2 + 2HCl \to MgCl_2 + 2H_2O$
$Mg(OH)_2 + 2HNO_3 \to Mg(NO_3)_2 + 2H_2O$
$Ba(OH)_2 + 2HCl \to BaCl_2 + 2H_2O$
$Ba(OH)_2 + 2HNO_3 \to Ba(NO_3)_2 + 2H_2O$
$Cu(OH)_2 + 2HCl \to CuCl_2 + 2H_2O$
$Cu(OH)_2 + 2HNO_3 \to Cu(NO_3)_2 + 2H_2O$
$Al(OH)_3 + 3HCl \to AlCl_3 + 6H_2O$
$Al(OH)_3 + 3HNO_3 \to Al(NO_3)_3 + 6H_2O$
c)
$Mg(OH)_2 \xrightarrow{t^o} MgO + H_2O$
$2Al(OH)_3 \xrightarrow{t^o} Al_2O_3 + 3H_2O$
$Cu(OH)_2 \xrightarrow{t^o} CuO + H_2O$