**Core Concept**
Meningococci (Neisseria meningitidis) and gonococci (Neisseria gonorrhoeae) are two closely related species of pathogenic bacteria that differ in their virulence factors, particularly the presence of a polysaccharide capsule. The capsule is a key virulence factor that enables meningococci to evade the host's immune system and cause meningitis.

**Why the Correct Answer is Right**
The correct answer is **B. Possess a capsule**. Meningococci produce a polysaccharide capsule that is composed of sialic acid and other sugars. This capsule is crucial for the bacterium's ability to cause invasive disease, including meningitis and septicemia. In contrast, gonococci lack a capsule and are generally less virulent. The capsule of meningococci is a major target for vaccines and therapeutic interventions.

**Why Each Wrong Option is Incorrect**
**Option A:** Meningococci are actually extracellular bacteria, as they are unable to survive and replicate within host cells. In contrast, gonococci can invade and survive within host cells.
**Option C:** Both meningococci and gonococci can ferment glucose, so this characteristic is not a distinguishing feature between the two species.
**Option D:** Both meningococci and gonococci are oxidase positive, meaning that they produce the enzyme cytochrome c oxidase, which is essential for their respiratory metabolism.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the presence of a capsule in meningococci is a critical determinant of their virulence and the severity of disease they cause. Vaccination against meningococcal capsular polysaccharides is an effective strategy for preventing invasive disease.

**✓ Correct Answer: B. Possess a capsule**