In the IUPAC system
of nomenclature, alkyl halides are named as halosubstituted hydrocarbons For mono halogen substituted derivatives of benzene, common and IUPAC
names are the same For dihalogen derivatives, the  prefixes o-, m-, p- are
used in common system but in IUPAC system, as you have learnt in Class
XI, the numerals 1,2; 1,3 and 1,4 are used 6