## Core Concept
Putrefaction refers to the decomposition process of organic matter, particularly in the context of a deceased body. Various factors, including environmental conditions and the presence of certain chemicals, can influence the rate of putrefaction. In the context of poisoning, certain substances can delay or accelerate this process.

## Why the Correct Answer is Right
The correct answer, **Arsenic**, is known to delay putrefaction. Arsenic acts by disrupting cellular processes and can inhibit the growth of bacteria and other microorganisms that are responsible for the decomposition of the body. By reducing microbial activity, arsenic poisoning can slow down the putrefaction process, making it a preservative-like effect on the body.

## Why Each Wrong Option is Incorrect
- **Option A: Lead**: Lead poisoning primarily affects the hematopoietic, nervous, gastrointestinal, and renal systems. It does not have a significant preservative effect on the body that would notably delay putrefaction.
- **Option B: Mercury**: Mercury is a potent toxin that affects various bodily systems, including the nervous, renal, and gastrointestinal systems. Like lead, it does not have a well-documented effect on delaying putrefaction.
- **Option D: Cyanide**: Cyanide acts rapidly by inhibiting cellular respiration. While it is highly toxic and can cause rapid death, its effect on putrefaction is not notably delayed compared to arsenic.

## Clinical Pearl / High-Yield Fact
A key point to remember is that arsenic has been historically used as a preservative, and its presence in a body can significantly delay the process of putrefaction. This can sometimes complicate forensic investigations, as the body may appear more preserved than expected given the post-mortem interval.

## Correct Answer: C. Arsenic