**Core Concept**
In forensic medicine, the examination of firearms and their projectiles (bullets or cartridges) is crucial for reconstructing crime scenes and linking evidence to suspects. The number of bullets or cartridges fired from a gun can be an important clue in forensic investigations. In this context, the term "tandem bullet" refers to a specific pattern of bullet discharge.

**Why the Correct Answer is Right**
A tandem bullet typically involves two bullets fired from the same gun in rapid succession, often as a result of a single trigger pull. This phenomenon occurs when the first bullet is still in the barrel when the second bullet is fired, resulting in the second bullet being propelled out of the gun alongside or immediately after the first bullet. This is due to the residual pressure and gases still present in the barrel after the first bullet's discharge. The tandem bullet pattern is often observed in forensic analysis and can be used to determine the type of firearm used and the sequence of events at a crime scene.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because a single bullet discharge is not referred to as a tandem bullet in forensic medicine.
**Option C:** Incorrect because three bullets fired from a single trigger pull is not a recognized tandem bullet pattern.
**Option D:** Incorrect because four bullets fired from a single trigger pull is not a known tandem bullet pattern in forensic medicine.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, the examination of firearms and their projectiles should always consider the possibility of tandem bullet discharge, which can significantly impact the interpretation of crime scene evidence.

**✓ Correct Answer: B. 2**