The correct answer is: Addition reaction.
In an addition reaction, two or more molecules combine to form a larger molecule. In the case of adding chlorine to benzene, the chlorine atoms add to the benzene ring to form chlorobenzene.
An elimination reaction is a type of chemical reaction that involves the removal of two groups from a molecule, usually forming two new bonds. In the case of benzene, an elimination reaction would involve the removal of hydrogen and chlorine atoms from the benzene ring to form ethylene.
A substitution reaction is a type of chemical reaction that involves the replacement of one group in a molecule with another group. In the case of benzene, a substitution reaction would involve the replacement of a hydrogen atom in the benzene ring with a chlorine atom to form chlorobenzene.
Therefore, the correct answer is Addition reaction.