First chlorinated insecticide

Options

A. DDT
B. gammaxene
C. iodoform
D. freon

Explanation

### Step-by-Step Solution:

1. **Identify the Question**: The question asks for the first chlorinated insecticide.

2. **Understanding DDT**: The full name of DDT is Dichlorodiphenyltrichloroethane. The name indicates that it is a chlorinated compound, specifically containing chlorine atoms.

3. **Chemical Structure**:
- The term "trichloro" indicates that there are three chlorine atoms in the molecule.
- The "diphenyl" part refers to the presence of two phenyl rings attached to the ethane backbone.

4. **Historical Context**:
- DDT was synthesized in 1874 by Austrian chemist Othmar Ziegler.
- Its insecticidal properties were discovered later in 1939 by Paul Muller.

5. **Examine Other Options**:
- **Gamaxine**: Its formula is C6H6Cl6, and while it is chlorinated, it is not the first chlorinated insecticide.
- **Iodoform**: The formula is CHI3, which contains iodine, not chlorine, and is used as an antiseptic, not an insecticide.
- **Freon**: The formula CCl2F2 indicates it is a refrigerant, not an insecticide.

6. **Conclusion**: Based on the analysis, DDT is confirmed as the first chlorinated insecticide.

### Final Answer:
The first chlorinated insecticide is DDT (Dichlorodiphenyltrichloroethane).

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