## Core Concept
The question pertains to the forensic analysis of firearm injuries, specifically the characteristics of entry wounds. **Entry-wound blackening**, also known as tattooing or stippling, is a crucial forensic feature. It results from unburned gunpowder grains and other debris being embedded into the skin.

## Why the Correct Answer is Right
The correct answer, **C. soot**, is related to the combustion products of the firearm discharge. When a firearm is discharged, it produces not only the bullet but also gases, flame, and unburned or partially burned gunpowder. Soot, which is a product of incomplete combustion, can deposit around the entry wound, especially if the firearm is discharged at close range. However, the specific term "blackening" in forensic pathology often refers to the embedding of unburned gunpowder grains into the skin, which appears as a black or dark discoloration. This phenomenon occurs due to the close-range discharge of a firearm, embedding particles into the skin.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is blank and cannot be evaluated.
- **Option D:** This option is blank and cannot be evaluated.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the presence of **soot** or **tattooing (stippling)** around a wound can help estimate the range of fire. Close-range shots are more likely to produce these effects. The absence of such markings can suggest a more distant shot. This differentiation is critical in forensic investigations to reconstruct the events surrounding a gunshot injury.

## Correct Answer Line
**Correct Answer: C. soot**