$a) C_6H_6+HNO_3 đ\xrightarrow{H_2SO_4đ,t°} C_6H_5NO_2+H_2O$

$C_6H_5NO_2+Cl_2\xrightarrow{FeCl_3,t°} m-Cl-C_6H_4-NO_2+HCl$

$b) C_6H_6+Cl_2\xrightarrow{FeCl_3,t°}C_6H_5Cl+HCl$

$C_6H_5Cl+HNO_3 đ\xrightarrow{H_2SO_4đ,t°} o-Cl-C_6H_4-NO_2+H_2O$

$c)C_6H_6+Br_2\xrightarrow{FeBr_3,t°}C_6H_5Br+HBr$

`C_6H_5Br+KCN->C_6H_5CN+KBr`

`C_6H_5CN+2H_2O+HCl->C_6H_5COOH+NH_4Cl`

$C_6H_5COOH+Br_2\xrightarrow{FeBr_3,t°} m-Br-C_6H_4-COOH+HBr$

$d) C_6H_6+Br_2\xrightarrow{FeBr_3,t°}C_6H_5Br+HBr$

$C_6H_5Br+HNO_3 đ\xrightarrow{H_2SO_4đ,t°} o-Br-C_6H_4-NO_2+H_2O$

`o-Br-C_6H_4-NO_2+3Fe+6HCl->o-Br-C_6H_4-NH_2+3FeCl_2+2H_2O`

$o-Br-C_6H_4-NH_2+NaNO_2+2HCl\xrightarrow{0-5°C} o-Br-C_6H_4-N_2Cl+NaCl+2H_2O$

$o-Br-C_6H_4-N_2Cl+CuCN\rightarrow o-Br-C_6H_4-CN+N_2+Cl^{-}$

`o-Br-C_6H_4-CN+2H_2O+HCl->o-Br-C_6H_4-COOH+NH_4Cl`