a, $Ca$, $K_2O$.
$Ca+2H_2O\to Ca(OH)_2+H_2$
$K_2O+H_2O\to 2KOH$
b, $Ca$, $Zn$, $Al_2O_3$ $K_2O$, $NaOH$, $Cu(OH)_2$, $CaCO_3$, $AgNO_3$.
$Ca+2HCl\to CaCl_2+H_2$
$Zn+2HCl\to ZnCl_2+H_2$
$Al_2O_3+6HCl\to 2AlCl_3+3H_2O$
$K_2O+2HCl\to 2KCl+H_2O$
$NaOH+HCl\to NaCl+H_2O$
$Cu(OH)_2+2HCl\to CuCl_2+2H_2O$
$CaCO_3+2HCl\to CaCl_2+CO_2+H_2O$
$AgNO_3+HCl\to AgCl+HNO_3$
c, $Zn$, $Al_2O_3$, $AgNO_3$, $CuCl_2$.
$Zn+2KOH\to K_2ZnO_2+H_2$
$Al_2O_3+2KOH\to 2KAlO_2+H_2O$
$2AgNO_3+2KOH\to Ag_2O+2KNO_3+H_2O$
$CuCl_2+2KOH\to Cu(OH)_2+2KCl$