We have to explain monochlorination.
Monochlorination is the process to introduce one chlorine atom in any organic compound.
Generally, monochlorination takes place by replacement of proton from organic compound. To do chlorination, Cl₂ or HCl is used as reagent.
Inntroduction of one Cl-atom in any organic molecule takes place through free radical mechanism.
The monochlorination of benzene is shown here: