`a) NaOH, Cu(OH)_2, Ba(OH)_2`
`NaOH + HCl -> NaCl + H_2O`
`Cu(OH)_2 + 2HCl -> CuCl_2 + 2H_2O`
`Ba(OH)_2 + 2HCl -> BaCl_2 + 2H_2O`
`b) Cu(OH)_2`
$Cu(OH)_2 \xrightarrow{t^o} CuO + H_2O$
`c) NaOH, Ba(OH)_2`
`2NaOH + CO_2 -> Na_2CO_3 + H_2O`
`NaOH + CO_2 -> NaHCO_3`
`Ba(OH)_2 + CO_2 -> BaCO_3 + H_2O`
`Ba(OH)_2 + 2CO_2 -> Ba(HCO_3)_2`
`d) NaOH, Ba(OH)_2`
