The insecticide Gammexane is:
A. DDT
B. Benzene hexachloride
C. Parathion
D. Chloral

Hint- Here in order to proceed this question, we must know all the four concepts individually and its properties to compare and get the required result.

Complete answer:

Gammexane is commonly known as Benzene hexa-chloride (BHC) which is used as an insecticide. Benzene hexa-chloride was first prepared in1825, the insecticidal properties were identified in 1944 with gamma isomers.
The chemical addition of chlorine to benzene produces a mixture of several stereoisomers of 1, 2, 3, 4, 5, 6 – hexa-chloro-cyclo-hexane. More volatile than DDT, BHC has a faster but less protracted action upon insects.
Gammexane is also known as lindane. The chemical formula of benzene hexa-chloride is ${C_6}{H_6}C{I_6}$. Benzene hexa-chloride is a colorless solid with a slight musty odor. It is an organochlorine chemical and as treatment for scabies and lice.
Preparation of Benzene hexa-chloride-
Chlorine combines with benzene, in the presence of sunlight and in the absence of oxygen as well as substitution catalysts, to form hexa-chlorocyclo-hexane.
DDT is dichlorodiphenyltrichloroethane which is a chemical compound. Though it is an insecticide but not Gammexane.
Parathion is an organophosphate insecticide on crops but it is not known as Gammexane.
Chloral is trichloroethanal which is the organic compound with colourless oily liquid that is soluble in a wide range of solvents.
As we can see that only Benzene hexa-chloride is known as Gammexane.

Therefore, option B is correct.

Note- While solving this question, we must know all the four concepts i.e. DDT, Chloral, Parathion, Benzene hexa-chloride. Also we must know all the insecticides and its chemical names to solve this question as one of the insecticide i.e. Gammexane is asked in this question.