Right answer is (a) Gamma BHC
For explanation: Gamma BHC and DDT are the most common insecticide used in India. DDT are a group of organochlorine insecticide. Bethrin is a group of Pyrethroids, Diuron is a group of phenyl urea pesticide, Mameb are basically group of organometallic compounds. These all are group of pesticides but not categorized as organochlorine insecticide.