## Core Concept
Post-mortem staining, also known as livor mortis or post-mortem lividity, is the discoloration of the skin due to the pooling of blood in the dependent parts of the body after death. This phenomenon occurs because the heart stops beating, and gravity causes the blood to settle. The duration for which post-mortem staining persists can give clues about the post-mortem interval.

## Why the Correct Answer is Right
The correct answer indicates that post-mortem staining persists for about 8-12 days if the body is left undisturbed. This duration can vary depending on environmental factors such as temperature, but generally, livor mortis becomes fixed and visible within a few hours after death and can persist for several days. The process involves the breakdown of the blood and its components, which eventually gets organized and becomes a part of the decomposition process.

## Why Each Wrong Option is Incorrect
- **Option A:** This option suggests a very short duration, which is incorrect because post-mortem staining does not resolve that quickly.
- **Option B:** This option might seem plausible but is not accurate for the persistence of post-mortem staining.
- **Option C:** This option suggests a longer duration than typically observed for the persistence of distinct post-mortem staining.

## Clinical Pearl / High-Yield Fact
A key point to remember is that post-mortem staining can be an important clue in forensic pathology. It typically becomes visible within 30 minutes to 2 hours after death and can change the appearance of the skin, making it purplish or blue in dependent areas. The presence and characteristics of livor mortis can help estimate the post-mortem interval and are influenced by factors like ambient temperature and the position of the body.

**Correct Answer: D. 8-12 days**