Dear student,
Dehydrohalogenation reaction is a process like decomposition reaction in which branched series of haloalkanes are broken to form alkene and alkynes.
Remember here the most important reagent is used which is KOH.
C2H5Cl + KOH = C2H4 + H2O + KCl
C2H5Br + KOH = ​ C2H4 + H2O + KBr
Regards