a)
PTHH:
$BaCl_2+2AgNO_3\xrightarrow{}Ba(NO_3)_2+2AgCl↓$
$NaCl+AgNO_3\xrightarrow{}AgCl↓+NaNO_3$
$BaCl_2+Na_2SO_4\xrightarrow{}BaSO_4↓+2NaCl$
$Ba(NO_3)_2+Na_2SO_4\xrightarrow{}BaSO_4↓+2NaNO_3$
b)
$MgCl_2+2KOH\xrightarrow{}Mg(OH)_2↓+2KCl$
$FeCl_3+3KOH\xrightarrow{}Fe(OH)_3↓+3KCl$
c)
$MgCl_2+2NaOH\xrightarrow{}Mg(OH)_2↓+2NaCl$
$BaCl_2+Na_2CrO_4\xrightarrow{}BaCrO_4↓+2NaCl$
$CaCl_2+Na_2CrO_4\xrightarrow{}CaCrO_4↓+2NaCl$