$\huge{1.}$

`Fe_2O_3 +CO` $\longrightarrow$ `Fe+CO_2`

`=>``Fe_2O_3 +3CO` $\longrightarrow$ `2Fe+3CO_2`

`----------`

$\huge{2.}$

`Fe_3O_4 + HCl` $\longrightarrow$ ` FeCl_2 + FeCl_3 + H_2O`

`=>Fe_3O_4 + 8HCl` $\longrightarrow$ `FeCl_2 + 2FeCl_3 + 4H_2O`

`----------`

$\huge{3.}$

`FeS_2 + O_2` $\longrightarrow$ `Fe_2O_3 + SO_2`

`=>2FeS_2 + 4O_2` $\longrightarrow$ `Fe_2O_3 + 4SO_2`

`----------`

$\huge{4.}$

`C_2H_5OH + O_2` $\longrightarrow$ `CO_2 + H_2O`

`=>C_2H_5OH + 3O_2` $\longrightarrow$ `2CO_2 + 3H_2O`

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