**Core Concept**
Para-para DDT refers to the para-isomer of dichlorodiphenyltrichloroethane, a synthetic insecticide used to control mosquitoes and other insects. The para-isomer is the most stable and toxic form of DDT, responsible for its environmental persistence and biological activity.

**Why the Correct Answer is Right**
The correct answer is the percentage of para-para isomer in technical-grade DDT, which is a mixture of various isomers. The para-para isomer is the most stable and predominant form in technical-grade DDT, accounting for approximately 93% of the mixture. This is due to the steric hindrance caused by the two chlorine atoms on the benzene rings, which makes the para-para isomer less susceptible to degradation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately represent the percentage of para-para isomer in technical-grade DDT.
* **Option B:** This option is incorrect because it overestimates the percentage of para-para isomer in technical-grade DDT.
* **Option C:** This option is incorrect because it underestimates the percentage of para-para isomer in technical-grade DDT.

**Clinical Pearl / High-Yield Fact**
The use of DDT has been largely phased out due to its environmental persistence and potential health risks, including cancer and neurological effects. The Stockholm Convention, an international treaty, aims to eliminate the production and use of DDT and other persistent organic pollutants.

**Correct Answer: C. 93%**