## Core Concept
Post-mortem staining, also known as livor mortis or post-mortem lividity, refers to 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 is no longer pumping blood, and gravity causes the blood to settle.

## Why the Correct Answer is Right
The correct answer indicates that post-mortem staining persists for a specific duration if the body is left undisturbed. Livor mortis typically becomes visible within 30 minutes to 2 hours after death and can persist for **about 8-12 hours** before it starts to fade or become fixed. The duration for which it persists can give clues about the time since death.

## Why Each Wrong Option is Incorrect
- **Option A:** This option suggests a very short duration, which is incorrect because post-mortem staining typically takes some time to develop and persist.
- **Option B:** This option might suggest a shorter duration than what is typically observed for the persistence of post-mortem staining.
- **Option C:** This option might suggest a longer or shorter duration but is not the best answer based on the typical persistence of post-mortem staining.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the presence and characteristics of livor mortis can help estimate the post-mortem interval (PMI), which is crucial in forensic investigations. However, it's also important to note that livor mortis can be influenced by several factors, including the environment and the condition of the body.

## Correct Answer Line
**Correct Answer: C. 8-12 hours.**