`a)`

phân loại:

`+` base : 

`-` `Fe(OH)_3` : iron (III) hydroxide

`+` acid có O

`-` `H_2SO_4`: sulfuric acid

`+` muối:

`-` `KNO_3` : potassium nitrate

`+` acidic oxide:

`-` `CO_2`: carbon dioxide

`b)`

`+` acidic oxide:

`-` `CO_2` : carbon dioxide

`+` base

`-` `Fe(OH)_3` : iron (III) hydroxide

`+` acid có O:

`-` `H_2CO_3` : carbonic acid

`+` muối

`-``Na_2SO_4`: sodium sufate

Đáp án + Giải thích các bước giải:

$a\big)$

$H_2SO_4:$ acid / sulfuric acid 

$Fe(OH)_3:$ base / iron (III) hydroxide

$KNO_3:$ muối / potassium nitrate

$CO_2:$ oxide acid / carbon dioxide

$b\big)$

$CO_2:$ oxide acid / carbon dioxide

$Fe(OH)_3:$ base / iron (III) hydroxide

$H_2CO_3$ acid / carbonic acid 

$Na_2SO_4:$ muối / sodium sulfate