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 1 3
Compounds
Containing
sp2 C—X
Bond
The dihaloalkanes having the same type of halogen atoms are named
as alkylidene or alkylene dihalides