Gammaxene (lindane), D.D.T. and bleaching powder are all important industrial and agricultural compounds of which halogen element?

Introduction / Context:
Many industrial and agricultural chemicals are compounds of halogens, a group of reactive nonmetals that includes fluorine, chlorine, bromine, iodine and astatine. The question mentions three well known substances: gammaxene, also called lindane, D.D.T., and bleaching powder. It asks which element they have in common. Recognising the halogen associated with these compounds helps in understanding their properties, uses and environmental impacts.

Given Data / Assumptions:

• Gammaxene or lindane is a chlorinated hydrocarbon insecticide based on hexachlorocyclohexane.
• D.D.T. is dichlorodiphenyltrichloroethane, a heavily chlorinated pesticide.
• Bleaching powder is calcium oxychloride, containing hypochlorite and chloride.
• The question asks which element is common to all of them.

Concept / Approach:
The common feature among these substances is the presence of chlorine atoms. Lindane has several chlorine atoms attached to a cyclohexane ring. D.D.T. has multiple chlorine atoms attached to aromatic rings and an aliphatic chain. Bleaching powder contains hypochlorite and chloride ions, both of which involve chlorine in different oxidation states. Chlorine compounds are widely used as disinfectants, bleaching agents and pesticides, but they can also have environmental and health concerns. The approach is to recall the names and compositions of these chemicals and identify chlorine as the shared element.

Step-by-Step Solution:
Step 1: Recognise that gammaxene or lindane is the gamma isomer of hexachlorocyclohexane, which clearly contains six chlorine atoms. Step 2: Recall that D.D.T. stands for dichlorodiphenyltrichloroethane, whose name itself indicates multiple chlorine atoms. Step 3: Bleaching powder is essentially calcium oxychloride, containing Ca(OCl)Cl, where OCl⁻ and Cl⁻ are chlorine based ions. Step 4: Nitrogen and phosphorus are not the main elements that define these compounds, although other groups may be present. Step 5: Therefore the common element forming these compounds is chlorine.

Verification / Alternative check:
Chemical formulas provide a direct check. Lindane can be written as C6H6Cl6, which contains six chlorine atoms. D.D.T. has the formula C14H9Cl5, again showing five chlorine atoms. Bleaching powder is often represented as Ca(OCl)Cl or a mixture containing CaCl2 and Ca(OCl)2. All of these representations contain chlorine. Reference to chemistry texts or safety data sheets confirms that chlorine chemistry is central to their function as insecticides and bleaching agents.

Why Other Options Are Wrong:
Option A, nitrogen, is common in many organic compounds but is not the defining element in these particular substances. Option B, phosphorus, appears in some pesticides and matches names like organophosphates, not D.D.T. or lindane. Option D, sulphur, is present in some fungicides and drugs but not as the key element in the compounds listed here. Option E, fluorine, is used in other fluorinated pesticides and refrigerants but does not characterise gammaxene, D.D.T. or bleaching powder. Only option C, chlorine, is consistently present in all three chemicals.

Common Pitfalls:
Students may be distracted by the fact that nitrogen and phosphorus are essential elements in agriculture and might think they must be involved in pesticides. However, the names and formulas of gammaxene and D.D.T. clearly point to chlorine. Another pitfall is to focus on the bleaching action of bleaching powder and forget that it is due to chlorine containing species like hypochlorite. Always pay attention to prefixes such as chloro and to chemical formulas when identifying common elements.

Final Answer:
The correct common element is Chlorine, which is present in gammaxene, D.D.T. and bleaching powder as part of their chemical structure.