## **Core Concept**
The question pertains to the composition of DDT (Dichlorodiphenyltrichloroethane), a well-known synthetic insecticide. DDT is a mixture of isomers, with the para-para isomer being the most relevant for its insecticidal activity. The chemical structure and isomeric composition of DDT are critical for understanding its properties and effects.

## **Why the Correct Answer is Right**
The correct answer, , indicates that the percentage of the para-para isomer in DDT is 40%. DDT is primarily composed of several isomers, but the para-para isomer, also known as p,p'-DDT, is the most active and desired form for insecticidal purposes. This isomer is responsible for the insecticidal activity of DDT, acting on the nervous system of insects. The specified percentage of 40% for the para-para isomer reflects the typical composition of technical-grade DDT.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This option is incorrect because it suggests a different percentage that does not accurately represent the para-para isomer content in DDT.
- **Option B:** - Similarly, this option does not correctly represent the percentage of the para-para isomer in DDT.
- **Option D:** - This option also provides an incorrect percentage for the para-para isomer content.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the effectiveness and environmental impact of DDT are closely related to its isomeric composition, particularly the content of the para-para isomer. This knowledge is crucial in pharmacology and toxicology for understanding the mechanisms of action and potential environmental hazards of insecticides like DDT.

## **Correct Answer:** .